Photoluminescence Properties of White Light Emitting Kbapo4:Dy3+ Phosphor

International Journal Of Advanced Engineering Science And Research Technology and Society for Technologically Advanced Materials of India –STAMI, India vol.1 (2016)

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Photoluminescence Properties of White Light Emitting Kbapo4:Dy3+ Phosphor

1Govind B. Nair and

1S. J. Dhoble*

1Department of Physics, R.T.M. Nagpur University, Nagpur, India- 440033, INDIA.

*Corresponding author email ID: [email protected]

ABSTRACT:

KBaPO4:xDy3+ (x= 0.005, 0.01, 0.02, 0.03) phosphors were effectively synthesized by sol-gel

method. The photoluminescence spectra exhibited an increasing behaviour in the emission intensity

with an increasing dopant concentration with optimum intensity at x = 0.03 moles and no

luminescence quenching was observed till this concentration. For the emission wavelength 576 nm,

the phosphor showed excitation peaks at 326 nm, 350 nm, 365 nm, 388 nm, and 426 nm. Highest

emission intensities were observed for an excitation wavelength of 350 nm. The emission

wavelengths showed two sharp peaks with their wavelengths centered at 484 nm (blue) and 576 nm

(yellow) corresponding to 4F9/2 → 6H15/2 transitions and 4F9/2→ 6H13/2 transitions respectively.

Keywords: Phosphor, phosphate, White light emission, Dy3+

INTRODUCTION

ABPO4 phosphors have made a huge impact in the field of luminescence with their versatile

properties [1–4]. Phosphate phosphors are known specially for their role as excellent host matrix

offering good luminescence efficiency, strong absorption in the VUV region, high chemical and

thermal stability, moderate phonon energy, exceptional optical damage threshold and low sintering

temperature [5]. As a result, phosphates are preferred over sulphides, sulphates, fluorides, nitrides,

etc. as host matrix to luminescence materials.

Rare earth doped phosphors are primarily sought for their ability to produce visible light

emission under UV or near-UV excitation. A number of rare earth doped phosphors are being

studied for their application in solid state lighting. It is possible to obtain white light from a single

component phosphor by using the principle of energy transfer from the sensitizer to the activator,

which has been introduced into a crystalline host matrix. White light can also be obtained by

adjusting the yellow to blue intensity ratio obtained by doping the host matrix with Dy3+ ion, as it

has two intense emission bands in the blue (470–500 nm) and yellow region (560–600 nm). In this

work, KBaPO4:Dy3+ phosphors have been synthesized by so-gel method and their

photoluminescence properties have been analyzed.

EXPERIMENTAL

KBa1-xPO4:xDy3+ (x = 0.0005, 0.01, 0.02 and 0.03) phosphors were synthesized by sol-

gel method. The starting materials were NaNO3, Ba(NO3)2, NH6PO4, Dy2O3, Polyethylene

Glycol (PEG, molecular weight = 1500) and Citric acid. Dy2O3 was dissolved in conc. HNO3

under heating and stirring, and a clear solution of Dy(NO3)3 was attained. All the four solutions

NaNO3, Ba(NO3)2 and NH6PO4 dissolved in deionized distilled water were added one by one in a

glass beaker and kept for stirring at a constant rate. 0.1 M solution of PEG and citric acid solution

were added to the above solution (molar ratio of Metal ions : Citric acid : PEG = 1:0.5:0.5). The

mailto:[email protected]


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solution was kept stirring and heating at 80 oC until the gelation takes place. The gel was dried in an

oven at 100 oC and the gel burnt into dry dark brownish precursor. This was then transferred into

porcelain crucibles and then heated in a muffle furnace at 600 oC for 6 hours. The resultant white

phosphor powder samples were then characterized for their photoluminescence properties. The as-

prepared phosphors were characterized by Shimadzu RF-5301PC Spectrofluorophotometer with a

slit width of 1.5 nm.

RESULTS AND DISCUSSION

Fig. 1 shows the PL excitation spectra of KBaPO4:Dy3+ phosphors monitored at 576 nm.

The sharp excitation peaks from 300 nm to 450 nm can be attributed to the intra-4f forbidden

transitions from the ground state 6H15/2 to higher energy levels of Dy3+. The peaks located at 326

nm, 350 nm, 365 nm, 388 nm, and 426 nm can be attributed to the transition from 6H15/2 to

4M17/2, 6P7/2, 6P5/2, 4P7/2 and 4G11/2, respectively. Optimum intensity was observed at 350 nm

indicating their potential to be used in UV LEDs.

Fig. 2 shoes the emission spectra of KBaPO4:xDy3+ (x= 0.005, 0.01, 0.02, 0.03) phosphors

at 350 nm excitation wavelength. The emission spectra displays similar trend for all the emission

lines and two dominating peaks at 484 nm and 576 nm, corresponding to 4F9/2 → 6H15/2 and

4F9/2 → 6H13/2 transition, respectively. It can be seen from the spectra that the blue emission is

stronger than the yellow emission, indicating that Dy3+ are located in centrosymmetrical site in

KBaPO4 [6]. It is observed that the emission intensities increase with Dy3+ concentration and reach

the optimum value at x = 0.03. No concentration quenching phenomenon was observed upto 3

mol% doping of Dy3+ ions in KBaPO4 phosphors.

Fig. 1: PL Excitation spectrum of KBaPO4:Dy3+ phosphor.


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Fig. 2: PL emission spectra of KBaPO4:Dy3+ phosphor.

CONCLUSIONS

A series of novel bluish-white light emitting KBaPO4:Dy3+ phosphors were synthesized by

the sol-gel method. Under the excitation of 350 nm, the phosphor gave two intense emission bands

centered at 484 nm and 576 nm corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2

respectively. Optimum concentration of Dy3+ for KBaPO4:Dy3+ phosphor was observed at x=0.03.

KBaPO4:Dy3+ phosphor can be confirmed as potential candidate for white light emitting diodes.

ACKNOWLEDGMENTS

One of the authors [GBN] acknowledges the Department of Science and Technology

(DST), New Delhi, INDIA for financial assistance under INSPIRE Fellowship programme with

registration number IF150675.

REFERENCES

[1]C.C. Lin, Z.R. Xiao, G.Y. Guo, T.S. Chan, R.S. Liu, Versatile phosphate phosphors ABPO4 in

white light-emitting diodes: Collocated characteristic analysis and theoretical calculations, J. Am.

Chem. Soc. 132 (2010) 3020–3028.

[2]H. FANG, S. HUANG, X. WEI, C. DUAN, M. YIN, Y. CHEN, Synthesis and luminescence

properties of KCaPO4:Eu2+,Tb3+,Mn2+ for white-light-emitting diodes (WLED), J. Rare Earths.

33 (2015) 825–829.

[3]L. Guan, C. Liu, X. Li, G. Jia, Q. Guo, Z. Yang, et al., Synthesis and optical properties of

KCaPO4:Eu2+ phosphor, Mater. Res. Bull. 46 (2011) 1496–1499.

[4]G.B. Nair, P.D. Bhoyar, S.J. Dhoble, Exploration of electron – vibrational interaction in the 5d

states of Eu2+ ions in ABaPO4 ( a = Li , Na , K and Rb ) phosphors, Luminescence. in press (2016)

doi.10.1002/bio.3143.

[5]G.B. Nair, S.J. Dhoble, Highly enterprising calcium zirconium phosphate [CaZr4(PO4)6 :Dy3+ ,

Ce3+ ] phosphor for white light emission, RSC Adv. 5 (2015) 49235–49247.

[6]S.-A. Yan, Y.-S. Chang, W.-S. Hwang, Y.-H. Chang, Enhancement of luminescence properties

via the substitution of Ba2+ by Sr2+ and Ca2+ in the white phosphors


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Single Crystal Growth and Dielectric Properties Of Gallium(Iii) Doped KDP By

Shankarnarayan- Ramasamy Method

N. S. Meshram, V.R. Raghorte@

,B. A. Shingade#,

*, N. M. Gahane , K. G. Rewatkar, V. M. Nanoti***

Department of Physics, Dr. Ambedkar College, Deekshabhoomi, Nagpur-10 India

@ Department of Physics, Model Arts and Science College, Karanja-33, India

# Department of Physics, Bhavbhuti Mahavidyalaya, Amgaon . 10India

***Department of applied Physics, Priyadarshani College of Engineering, Nagpur-10

Email :[email protected]

ABSTRACT

Potassium Dihydrogen Phosphate (KDP) is newly developed ideal nonlinear optical crystal used

for high-energy laser technology and optical electronic devices. Gallium ion doped KPD single

crystal grown by Shankarnarayan -Ramasamy method. Good and transparent qualities of crystals

have been harvested with dimension 11x10x13 cm .The crystal structure and perfection has been

determined using powder XRD and High resolution XRD. Presence of Gallium was confirmed by

EDAX in the crystals. Functional groups were present in the crystal by FTIR. Thermal properties of

the crystal have been studied by using Thermogravimetric (TGA) and Differtial thermal analysis

(DTA). Optical transparency has been studied by UV-VIS spectrum. Dielectric properties were

studied with varying frequency at different temperature.

Keyword: - single crystal growth, KDP, Powder XRD, FTIR, TGA-DTA, Dielectric ,EDA

INTRODUCTION

KH2PO4 (KDP) and KD2PO4 (DKDP) crystals are currently the only nonlinear materials

suitable for frequency converters and Pockels cells in high-power large-aperture laser systems.

These crystals often suffer from laser damage, which adversely affects the quality of the

downstream beam. The observed damage thresholds of KDP/DKDP crystals are much lower than

the intrinsic thresholds, due to the nano-scale impurities, which are difficult to identify due to their

sizes. Laser-induced bulk damage resistance of KDP/DKDP crystals strongly depends on the laser

wavelength. The laser damage threshold at 1064nm is much higher than that at 355 nm.[1]

Trivalent impurities like Fe 3+,

Cr 3+

, Al3+

have effect growth rate of the crystal. Due to there

comparable ionic size with potassium ion and probably substituted trivalent impurities. Ga 3+ ion is

optically active material and no study has been made to investigate the effect of Ga(III) ion on

growth and optical properties of KDP crystal. Present work is based on effect of trivalent on

growth and dielectric properties of crystal. SR method is most suitable method for unidirectional

growth with 100% solute conversion efficiency [2].

SHAKARNARAYAN RAMASAMY METHOD FOR SINGLE CRYSTAL GROWTH

S-R method is the unidirectional crystal growth method by slow evaporation of solution.

Seed crystals were prepared by convectional recrystallization slow evaporation method. KDP of

Merck AR grade was used to prepared seed crystal. Very good and transparent qualities of seed

crystals were selected having perfect external morphology. <100> crystal plane was selected for

unidirectional growth in S-R method. Seed crystal was cut carefully and polished portion along

<100> plane. The processed seed crystal has been placed at the bottom of ampule, which is special

designed for S-R method[3,4]. Solution was prepared at 30 oC according to solubility curve. 27.8



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gm/ 100 of KDP solute Merck AR grade has been dissolved in (Millipore 18.2 M Ohm cm

resistance) triple filter deionized water. Solution was kept three hours on magnetic stirrer at 30 oC

temperature for homogeneity in the solution. Solution was kept slightly under saturated for S-R

method. Clean filtered solution was carefully filled in ampoule without disturbing the position of

seed crystal inside the ampoule. The ampule has been rested in S-R set up for two hour. Initially,

temperatures are kept 30 oC at upper and lower ring heater. The solution has been settled inside the

ampule and concentration gradient maintain along the ampule. Concentration gradient was

maintained minimum at top and maximum at the bottom of the ampoule. Upper ring heater

temperature slightly was increased 35 oC for rising evaporation rate at top of the ampoule. The top

ring heater controls the spurious nucleation near the surface region of the solution during crystal

growth process. Upper part of ampule has been covered with transparency sheet and the small hole

at the center is reduced nucleation at upper part of ampule.

A transparent KDP crystal growth has been observed at the bottom of ampule under

optimizing condition in week. The KDP growth rate is approximately 1 mm per day was observed.

A good transparent quality of crystal was harvested. KDP Crystal growth has been carried out for

different doping concentration in S-R method [5].

Fig1. SR set up for growth crystal Fig 2 Grown KDP crystals by SR method

CHARACTERIZATION

Good quality and transparent KDP crystals were ground in pestle mortar to determine

different characterization. Some KDP crystals were cut in dimension 10mm x 10mm square area

for optical transmission studies.

1. Powder XRD and single crystal XRD analysis

Fig 3 powder XRD of KDP crystal

The crystalline phase characterization of the samples is carried out by a computer interfaced

X-ray Diffractometer (Philips, Xpert - MPD) operating at 40 kV and 30 mA with CuKα radiation

where =1.54056 Å. It is observed that the powder XRD diffracted peaks are same in the pure and

doped KDP crystal. The prominent peak of pure and doped KDP (101), (200), (112), (202), (310),


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(312) are observed. The sharp peak indicated that the crystalline natures of grown crystal are fine

quality. The XRD data matched with the JCPDF data file no 035-0807 and result shows that gallium

has entered into the KDP lattice. It shows that the crystal structure of KDP remains same by doping

gallium [6].

2. FTIR spectral analysis

An FTIR spectrum of pure and doped KDP crystal has been recorded on VARIAN resolution pro

FTIR spectrometer in the range 400- 6000 cm -1 by KBR pallet technique.

Fig 4 FTIR of KDP crystal

The assignments confirm the presence of various functional groups present in the material. The

wave number 3065,3334 cm -1is presence of O-H bond, 2919,2839,2461 cm-1 presence of P-O-H

bonding, 2358 cm -1 represent P-O=H bond, 1295,1100 cm -1 presence of P=O bond, 904 and 543

cm -1 is represent of P-O-H bond [7,8].

3. EDAX studies

Fig 5 EDAX of Gallium doped KDP crystal

Energy dispersive X-ray analysis (EDAX) used in conjunction with all types of electron

microscope has become an important tool for characterizing the elements present in the crystals[8].

In the present research module study, INCA 200 energy dispersive X-ray micro analyzer equipped

with LEO – Steroscan 440 Scanning electron Microscope, analyzed the crystal. The recorded

EDAX spectrum is shown in figure 6. Presence of Gallium is confirmed from the EDAX spectrum

[9,10].


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4. TGA -DTA Studies

0 100 200 300 400 500 600 700 800 900

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

82

84

86

88

90

92

94

96

98

100

340.36oc

318.18oc

275.52oc

Hea

t Flo

w E

ndo

Dow

n (m

W)

218.61oc

DTA

TGA

Wei

ght %

(%)

Temperature oc

Fig TGA- DTA Gallium doped KDP Crystal DTA and TGA of KDP were carried out with the help of an instrument (STA 409C) using

KDP crystals as sample and alumina as reference [11]. As shown in figure 7, KDP doped sample

were decomposed at 320.3 . The graphs show the peaks at 261.6 , 213.5 , 261.6 reveal

exothermic reaction due to escape of oxygen atoms from the KDP crystal. As shown in figure ,

TGA curve sharply decrease at temperature at 230 and 356 is most probable melting point

of KDP crystal TGA curve shows that crystals are thermally stable below 230 [12,13]

5. Dielectric studies

KDP has dielectric nature was measured by Wynne Kerr 6500B (UK) impedance analyzer.

At low frequency, it was observed that the dielectric constant increases with increase temperature.

Also, it is observed that the dielectric loss reduces with increase in doing concentration. At high

frequency the dielectric constant decreases to large extent. This peculiar behavior appears because

of dopant Ga+3 ions in the crystal lattice [14].

Fig 7 Dielectric constant vs. log frequency Fig 8 Dielectric constant vs. Temperature


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RESULT AND DISCUSSION

Pure and Trivalent Ga3+ ion added KDP crystals were grown by Shankarnarayan -

Ramasamy method. The XRD spectrum shows the excellent crystalline nature of Gallium added

KDP crystal. All functional groups were present in crystals and are confirmed by FTIR spectrum.

Ga3+ ions are adsorbed on the crystal faces and create isolated centers. The presence of

Gallium was confirmed by EDAX analysis. DTA, TGA analysis reveals that KDP is stable up to

240.36 before it melts. Gallium ion enhances the conductivity in crystal and Dielectric constant.

Dielectric constant is decreases with increase in frequency as temperature increases.

ACKNOWLEDGEMENT

Author N. S. Meshram and Dr. K. G. Rewatkar Acknowledge UGC for their financial support under

major research project

REFERENCE

[1]S. B. Monaco, L. E. Devis, S. P.Velsko, F. T.Wang, D. Eimerl, and A. Zalkin, J. Cryst. Growth

85, 252–25 (1987).

[2]N. P. Rajesh, V. Kannan, P. SanthanaRaghavan, P. Ramasamy, and C. W. Lan, “Nucleation

studies and crystal growth of (NH4)H2PO4 doped with thiourea in supersaturated aqueous

solutions,” Materials Chemistry and Physics, vol. 76, no. 2, pp. 181–186, (2002).

[3].N.P. Rajesh, V. Kannan, M. Ashok, K. Sivaji, P. SanthanaRagavan, P. Ramasamy,

[4].N. Balamurugan, P. Ramasamy, Cryst. Growth Design 6 1642(2006).

[5].Christer B. Aakeroy, Peter B. Hitchcock, J. Mater. Chem. 3 (11) 1129) (1993.6

[6].G.T. Moldazhanova, Crystallogr. Rep. 39 135(1994).

[7].A.A. Chernov, in: A.V. Shubnikov, N.N. Sheftal (Eds.), Growth of Crystals, vol. 3, Consultants

Bureau, New York, p. 35(1962).

[8].C. N. Banwell and E. M. McCash, Fundamentals of Molecular Spectroscopy, McGraw-Hill,

New York, NY, USA, 4th edition, (1994).


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Super-Paramagnetic Iron Oxide Nanoparticles for Hyperthermia Applications

N. N Sarkar* K.G Rewatkar1 V.M Nanoti

2 C.S.Prakash

3

*Department of Physics Dr. Ambedkar College Deeksha Bhoomi Nagpur 440010 1 Department of physics Dr. Ambedkar college Deeksha Bhoomi Nagpur-10

2Department of Applied Physics P I E T Hingna Nagpur 3Department of Applied Physics SJCI T Chickballapur Bengaluru

*Corresponding author, [email protected]

ABSTRACT

Today most of the Researchers are attracted on Super Paramagnetic Iron Oxide Nanoparticle

(SPION) material due to their novel application and unique magnetic properties and their uses in

nanotechnology. SPION with a spinel structure form a large group of materials with a broad range

of applications. When the ferrite materials exhibited superparamagnetic behavior then it can be

applicable for biological purposes like drug delivery, hyperthermia and MRI Therefore, the

superparamagnetism is a characteristic strongly desired for spinel ferrites. Since this phenomenon is

size-dependent, the methodologies to synthesize these materials have emerged as a crucial step in

order to obtain the desired properties. In this regarding, several synthetic processes have been

developed. For example, Auto combustion, co-precipitation is a fast and cheap method to synthesize

superparamagnetic spinel ferrites.

Keywords: spinel ferrite, SPION , hyperthermia, drug delivery, synthesis methods, etc.

INTRODUCTION

Metal oxide nanoparticles are the important class of materials as their optical, magnetic and

electrical properties find a wide range of high tech applications [1]. Fe3O4 nanoparticles are

common ferrite with an inverse cubic spinal structure. These class of compounds exhibit unique

electrical and magnetic properties due to the transfer of electrons between Fe2+ and Fe3+ on

octahedral sites [2]. Fe3O4 nanoparticles have been the subject of intense interest because of their

potential applications in several advance technological areas due to their promising physical and

chemical properties. Generally, these properties depend on the size and structure of particles [3,4].

Fe3O4 nanoparticles find wide applications in the field of biomedical, as anticancer agent [5,6],

corrosion protective Pigments in paints and coatings [7]. The magnetic atoms or ions in such solid

materials are arranged in a periodic lattice and their magnetic moments collectively interact through

molecular exchange fields, which give rise to a long-range magnetic ordering. Among all iron oxide

nanoparticles, Fe3O4 represent the most interesting properties due to of its unique structure i.e. the

presence of iron cations in two valence states, Fe2+, Fe3+ on tetrahedral and octahedral site with an

inverse cubic Spinel structure. The coercivity and remenance values for the super paramagnetic

nano Fe3O4. nanoparticles have been found to be zero by the earlier reported methods[8]. Presently,

cell labeling strategies find application of superparamagnetic ferrite either through conjugating the

magnetic nanoparticles to the cellular surface of the stem cell or by internalization of the particles

into the cell. Superparamagnetic ferrite can work in both of these ways, since the potential to

manipulate their surface chemistry is plentiful and their sizes along with other attributes promote

their successful uptake into cells. The superparamagnetic nano ferrites also interface well with MRI

technology. The use of superparamagnetic particles play a crucial role In the diagnostic imaging

modality technique finds application in the study of stem cell [9].



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SUPERPARAMAGNETISM

Soft ferrites are characterized by a small value of coercivity, so they cause low hysteresis

loss at high frequency. They are widely used in electromagnetic cores of transformers, switching

circuits in computers and radio-frequency (RF) inductors, e.g. lithium ferrite, nickel ferrite and

manganese–zinc ferrite. A typical hysteresis loop of a soft magnetic material a high magnetizing

force is encountered, a point is reached where further increase in, H, does not cause useful increase

in, B. This point is known as the saturation point of that material. The saturation flux density, Bs,

and the required magnetizing force, Hs, to saturate the core.( fig1)

Fig 1 A typical hysteresis loop of a magnetic material

Spinel Ferrite

Spinel ferrites are a huge group of materials with the same structure of the natural spinel

MgAl2O4. According to the literature [10], over 140 oxides and 80 sulphides were already

synthesized and their physicochemical properties studied. This large variety of spinels is due to their

capacity to incorporate cations with different charges into the structure. However, the total positive

charge should not be higher than 8 to balance to the charge of the anions. Another requirement is

about the cation radii. The values must be in the range of 0.4-0.9Å.Magnetic spinels usually have

the general formula of M2+Fe2O4 (or MO.Fe2O3), where the divalent cation can be Mn, Ni, Fe,

Co, Zn, Mg, etc. The most important and abundant is the natural Fe3O4 (or FeO.Fe2O3) [11]. The

crystalline structure of spinel ferrites was firstly determined by Bragg [12] In1915. In the spinel

structure, the metallic ions are coordinated to oxygen with two different ways, which generate two

coordination sites. The first one is called A site and the cation is coordinated in tetrahedral

symmetry. The second one, namely B sites, is coordinated in octahedral symmetry as shown in

figure 2


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Fig 2. Spinal structure

Hyperthermia

Hyperthermia is the cure harnessing the nature that a cancer tissue has less heat-resistant

than normal one. In the hyperthermia, it is important that the cancer tissue is selectively heated

without damaging the normal tissue. The interstitial hyperthermia using magnetic material is known

as Magnetic Induction Hyperthermia [13,14], Soft Heating [15] or Implant Heating System (IHS)

[16] is an excellent system to perform the purpose. In the system, the ferromagnetic material

(implant) is implanted in the cancer tissue at first,and it is heated by utilizing the eddy current or the

magnetic hysteresis loss under the high frequency alternating magnetic field (HFMF). Then, the

temperature of the cancer tissue is raised and regulated at a Curie temperature Tc of the implant

material. We previously reported on the mechanism of heat generation by the eddy current [17],

which depends on the magnetic field, the frequency of HFMF, the permeability, the resistivity and

the size of the implant. Moreover, in order to gain the maximum heat generation, it is necessary that

the direction of HFMF is parallel to the long axis of the implant. Fe–Pt alloy needles [18], which

were developed based on this concept, were used for treatments of brain tumors [19] and oral

malignant tumors [20]. On the other hand, the hysteresis loss is hardly dependent of the direction of

HFMF and of the size of the implant. Therefore, the materials heated by the magnetic hysteresis loss

can also be used for hyperthermia in a fine powdered form.

LITERATURE REVIEW

Won li Choiet al.(2012) [21] was studied the effect of mechanical properties of iron oxide

nanoparticle loaded functional nano-carrier on tumor targeting and imaging, and they conclude that

the mechanical properties of chitosan-functionalized, Pluronic based nano-carrier were

systematically varied by loading different amounts of IONPs, but still keeping the same size, shape,

surface charge, and release profile of the loaded IONP. Overall, very good tumor targeting and

accumulation of IONP were achieved by using the functional nano-carrier, thus, this could serve as

an enhanced MRI contrast agent. P.A. Desai et al.(2011) [22] were studied on Silver doped

lanthanum chromites by microwave combustion method and found that LaCrO3 and silver doped

lanthanum chromite nanoparticles have been synthesized by microwave combustion route. Pure

phase products are obtained at microwave power of 0.56 kW, irradiation time of 10 min and fuel to

oxidizer ratio of 1. Average size of LaCrO3 particles is 57 nm, while the silver doped samples have

a finer particle size of 7–8 and 20–26, respectively, for A site and B site doping. Increase in

coercivity and saturation magnetization values of doped samples is attributed to non magnetic


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nature of silver. Hasan Mukhtar et al.(2013) [23] also studied on Nanoformulation of natural

products for prevention and therapy of prostate cancer and they conclude that the use of naturally

occurring products, such as dietary nontoxic phytochemicals, has emerged as one important

approach to fight this disease, which may be appropriated for high-risk patients, especially those

with isolated HG-PIN, elevated PSA, and negative biopsy. Silvio Dutz et al.(2009) [24] were

studied on Ferrofluids of magnetic multicore nanoparticles for biomedical applications and they

found that the peak position from XRD data was used to distinguish between the magnetic phases

maghemite and magnetite. The diffractogram show a relatively broad single peak between the

theoretical angles for maghemite and magnetite. This means that the resulting particles presumably

consist of solid solutions of both phases (one resulting peak).

However, it is also possible that particles consist of a mix of maghemite and magnetite

particles (two separated peaks). In principle, a differentiation between these both cases is feasible,

but due to the peak broadening of the small particles, a superposition of both peaks is possible.

Pol-Edern Le Renard et al.(2011) [25] was studied on magnetic and in vitro heating properties of

SPIONs and they found that, The superparamagnetic properties of magnetic silica composite

microparticles embedding nanoscale maghemite iron oxides are preserved in the injectable

formulations for the whole range of concentrations that allow syringe ability. These properties also

remain preserved in the implants formed in situ. The magnetic properties as well as the heating

capacity, which improved with increase in particle fraction, can be extrapolated from the

concentration of magnetic microparticles. With these AMF parameters, a straightforward

determination of the dissipated heat is now possible. In association with the previous in vivo

studies, this further allows for the modeling of tissue heating in vitro and in vivo, and this

improves our understanding of the heated livery through formulations intended for magnetically

mediated hyperthermia in the treatment of solid tumors. Ahmad Gholami et al.(2015) [26] were

studied on Lipoamino Acid Coated Superparamagnetic Iron Oxide Nanoparticles Concentration

and Time Dependently Enhanced Growth of Human Hepatocarcinoma Cell Line. And they found

that the cytotoxic effects of naked and some surface coated SPION on hepatocarcinoma cells

revealed that SPION at lower concentrations can be beneficial for these cells because of their

nutrient effect.

However, at concentrations higher than 50 micro gram /mL the trend was reversed and the

cell viability was decreased. Generally, it was concluded that SPION have dual impact on Hep-

G2: cell growth promotion and toxicity. In the initial phase (at concentrations from 1 to 50 micro

gram /mL), the dominant mechanism is the former one; however, by increasing nanoparticles

concentration, cytotoxic effect progressively rises and eventually becomes the main mechanism, if

aggregation or sedimentation of particles did not happen. Surface modification of SPION

especially the ones coated with LAA’s can maintain growth-enhancing effect. The reason may be

the controlled release of ionic iron into the cells. Biocompatible LAA coated SPION can be used

as targeted delivery of materials for diagnostic and therapeutic purposes. Alexander L. Kovarski et

al. (2006) [27] studied on ESR of thermal demagnetization processes in ferromagnetic

nanoparticles and the results comes out that ESR data indicate that the process of thermal

demagnetization of the tested particles is very complex, and some magnetic ordering remains in

the particles even above the Curie temperature, measured by static magnetic measurements.

Processes of thermal demagnetization in the vicinity of the Curie temperature in the alloys and

manganites are significantly different. Further studies of the thermal demagnetization processes in

ferromagnetic nanoparticles and deeper understanding of their mechanisms are crucial for


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developing effective mediator particles for magnetic fluid hyperthermia with parametric feedback

for biological applications [28-29].

SYNTHESIS METHOD TO OBTAIN SPINEL FERRITE NPS

Spinel ferrites can display the SPM behavior at room temperature. This is a very special

condition demanded for applications in the biomedical field. However, it is necessary to have a very

smaller NPs size. In order to face this, the choice of the appropriate synthetic methodology is

fundamental. For example, classical solid state routes are not suitable because the higher

temperatures used normally lead for bigger NPs size. Therefore, some researchers have developed a

wide range of synthetic approaches towards spinel ferrites like Co-precipitation, Sol- Gel Auto

combustions, Hydrothermal, Solvothermal, Decomposition and Microwave synthesis etc.

CONCLUSIONS

1) The Iron Oxide based material should be design as multiphase composite such that it

shows the different magnetic properties from each phase. The Curie temperature is in between 40 -

500C so that it can be easily demagnetized. It should be single spin domain so that it is easily

oriented by external applied field

2) It is found from the literature the microwave combustion technique is the one of the

promising technique for preparation of sample with the possibility of utilizing cheap precursors,

short reaction time and nanocrystalline products.

3) Keep it in mind that the magnetic material should be biocompatible therefore researcher

also focuses on non toxicity and PH value of material

REFERENCES.

[1] L. Zhou, J. Xu, X. Li, F. Wang, Mater. Chem. Phys. 97 (2006) 137.

[2] R. Chen, G. Song, Y. Wei, J. Phys. Chem. C 114 (2010) 13409.

[3] G. Schmid, D. Fenske, Phil. Trans. R. Soc. A 368 (2010) 1207.

[4] M. L-r, W. Chen, Y. Tan, L. Zou, C. Chen, H. Zhou, Q. Peng, Y. Li, Nano Res. 4 (4) (2011)

370.

[5] J.K. Oh, J.M. Park, Prog. Polym. Sci. 36 (2011) 168.

[6] D. Pan, H. Zhang, T. Fan, J. Chen, X. Duan, Chem. Commun. 47 (2011) 908.

[7] J. Alam, U. Riaz, S.M. Ashraf, S. Ahmad, J. Coat. Technol. Res. 5 (2008) 123.

[8] N. Bao, L. Shen, Y. Wang, P. Padhan, A. Gupta, J. Am. Chem. Soc. 129 (2007)

[9] M. Mahmoudi, H. Hosseinkhani, M. Hosseinkhani, S. Boutry, A. Simchi, W.S

[10] R.J. Hill, J.R. Craig, G.V. Gibbs, Systematics of the spinel structure type, Physics and

Chemistry of Minerals 4 (1979)

[11] V.G. Harris, Modern Microwave Ferrites, IEEE Transactions on Magnetics 48 (2012)

[12] W.H. Bragg, The structure of magnetite and the spinels, Nature 95 (1915) 561.


14

Super Paramagnetic Behavior Of Mn Substituted Zn Ferrites Nanopartical Prepared

By Sol-Gel Auto Combustion Route

M. J. Gothe, A. P. Bhat, K. G. Rewatkar

Department of Physics, Dr. Ambedkar College, Nagpur-10 India

Department of Electronics, RTM Nagpur University, Nagpur-10 India

[email protected]

ABSTRACT

Manganese substituted zinc ferrite nanoparticals ( MnX Zn1-X Fe2O4with x = 0,0.5,1 ) were

synthesized via sol-gel auto combustion route. X-ray diffraction (XRD), transmission electron

microscopy (TEM), scanning electron microscopy (SEM), and electron dispersive X-ray (EDX)

have been used to investigate the prepared Magnetic Zinc Nanocrystal (MZN). Magnetic properties

of the prepared samples have been detected by vibrating sample magnetometer (VSM), at room

temperature and the results of the prepared MZN exhibits a superparamagnetic (SPM) behaviour.

SPM nanocrystals are promising applications in medical science such as drug delivery,

bioseperation and magnetic resonance imaging (MRI).

Keyword: Magnetic measurements, Superparamagnetism

INTRODUCTION

Spinal ferrites are most widely used magnetic material due to the low cost. Mn-Zn ferrites

have many important applications, particularly in electronics and engineering industry [19].

However, (MnX Zn1-X Fe2O4with x = 0.5, 1) exhibits superparamagnetic (SPM) behavior by using

the study of VSM. Superparamagnetism is a form of magnetism, which appears in small

ferromagnetic or ferrimagnetic nanoparticles. In nanoparticles, magnetization can randomly flip

direction under the influence of temperature. Typical time between two flips is called “Neel

relaxation time”. In the absence of external magnetic field, the time used to measure the

magnetization of the nanoparticals is much longer than the “Neel relaxation time”. Their

magnetization appears to be in an average zero. They are said to be in the Superparamagnetic state.

An external magnetic field is able to magnetize the nanoparticles. In paramagnetism, their magnetic

susceptibility is large.

SPM is not just an abstract topic of study in advance physics. But it also has a practical

applications in the medical field such as MRI technology, DNA & RNA experimentation treatment

of hyperthermia and drug delivery [1-10]. It is also used in high-tech sensors (of the sort used in

aerospace technology) and other aspect of nanotechnology. For high performance applications in

biomedicine, the magnetic nanocrystals are required to posses’ small width in proportion to length

distribution and uniform spherical shape that gives superparamagnetic properties [11, 12]

EXPERIMENTAL

Preparation of sample:

Powder of MZN ferrites particles were prepared by sol-gel auto combustion method. by

Using analytical grade chemical reagents of Mn(NO3)24H2O, Zn(NO3)26H2O, and

Fe(NO3)39H2O and its stoichiometric proportions were first dissolved in deionized water. The

mixture of solution was heated at 800c till the complete mixture transformed in to gel. The gel of



15

the solution which were ignited and burnt by microwave oven on 600 watt for 7 minute to obtain

ash powder. The powders were annealed slowly at 8000c in a furnace for 4 hours after intermediate

grinding.

Characterization Technique:

The phase identification and crystalline structural analysis of the thermally treated powder

was analyzed by X-ray diffraction (XRD, Bruker AXS D8 advance, Cu K radiation λ = 0.1540

nm). The size and morphology of such prepared samples were characterized by scanning electron

microscopy. (SEM, Camca SU, SEM probe) and transmission electron microscopy (TEM, Phillips,

CM-200) for magnetic hysteresis loops were measured using a vibrating sample magnetometer

(VSM. Lakeshore 7410).

RESULTS AND DISCUSSION:

Fig.1. a & b) shows XRD pattern and broading of high intensity peak

The crystalline structures of MZN were characterized by XRD as shown in above fig.1 (a)

& (b). All the Bragg’s reflections have been indexed which confirmed the formation of simple cubic

spinel structure in single phase without any impurity peak. The strongest reflection and broadening

of high intensity peak comes from the (311) planes as depicted by JCPDS card 74-2403. which

denote the spinel phase appearing at 35.070 & 35.110.The crystalline size were calculated for

(MnXZn1-XFe2O4with X = 0.5,1) using high intensity (311) peaks and using Scherer formula i.e.

dhkl = 0.9 /cos.The values are found to be15nm and 16 nm.The lattice parameter for

Mn0.5Zn0.5Fe2O4 and MnFe2O4 The values are found to be 8.4812 Å & 8.4699 Å. it was found

that the lattice parameter decreases with increasing cations substitution of Mn2+ due to difference

of ionic radius (ionic radius of Zn+2 is 1.35 Å & Mn+2 is1.40Å) and its atomic mass.

b


16

Fig .2 A typical TEM image of MnxZnxFe2O4, x =0.5,1 nanoparticles.

A typical TEM image of the prepared MZN nanocrystals has been shown in above fig.2. the

circular diffraction rings are clearly visible, indicating the nano crystalline nature of MZN. Most of

the such prepared magnetic nanocrystals are nearly spherical structure as per shown in TEM. Dark

regions are representative nanoparticles which are in agreement with the SEM findings below. The

morphogical studies of the Mn-Zn ferrite powder was carried out using SEM. This type of electron

microscope is capable of producing high resolution images of a sample surface [13-14] due to the

manner in which the images are created. SEM images have a characteristic three dimensional

appearance and are useful for judging the surface structure of Mn-Zn ferrite. It is found that the

powders were made up of particles with the size in the nano range as shown in fig.3. In which the

powder form of the solid sample was mounted on the conducting resin with dispersion treatment,

indicating that the almost spherical and homogeneous nanoparticles with the average size of MZN

are about 28 nm. This result is in agreement with the result of XRD and TEM analysis [17].

The chemical composition of such prepared ferrites samples was further confirmed by

energy-dispersive X-ray analysis (EDX). The result shows that Me2+/Fe3+ ratio is about 0.5 which

is in agreement with the expected stoichimetry in each case as shown in fig.3 EDX system are

attachment to SEM or TEM instrument where the imaging capability of the microscope identifies

the specimen of interest. The data generated by EDX analysis consist of spectra showing peak of

Mn, Fe, and O, corresponding to the elements making up the true composition of the sample being

analysed.The EDX technique is non-destructive and specimen of interest can be examined in

situation with little or no sample preparation.

Fig 3.SEM and EDX spectrum of the sample Mn Fe2O4

100nm

100nm

MnFe2O4


17

The magnetic properties of the prepared MZN were investigated with a VSM as shown in Fig.4.

Fig 4: Magnetization curve of nano crystalline MnXZn1-XFe2O4with X = 0.5,1. At room temp.

The magnetization curves measured at room temperature, from the curve the measured

magnetic saturation values are about 28 emu/g for Mn0.5Zn0.5Fe2O4 and 20 emu/g for MnFe2O4.

The corecivity of the as prepared magnetic nanocrystals at room temperature is negligible, because

in a nano size particals many single domains are uniformly magnetized with all the spins aligned in

the same direction. The magnetization will be in reversed spin rotation, since there are no domain

walls to move. I.e. this is the reason for the very high coercivity observed in thin research module

with reported values between 38 between 177 Gauss in small nano particles [18, 20]. The

superparamagnetic behaviour can be represented by hysteresis curve as shown in fig.4.

Superparamagnetism occurs in nanoferrites which are single domains i.e. composed of a single

magnetic domain. This is possible only when their diameter measures below 3-50 nm, depending on

the materials. Superparamagnetic materials do not retain any significant amount of magnetization in

the absence of externally applied magnetic field and thus do not form aggregates.

A curve between magnetization and applied field (20kG) at room temperature is shown in

fig.4. It shows typical superparamagnetic nature with no trace of hysteresis and coercivity 38G and

almost zero remanence. It also prominently showed non-attainment of saturation magnetization even

at 20KG.

The nonsaturation of M-H loop and the absence of hysteresis remanence and coercivity at

room temperature strongly suggests the presence of superparamagnetic behavior.The values of Ms

are higher in multidomain bulk ferrites (45 emu/g) [15], than the Mn-Zn compounds represented in

the present work (Ms=28 emu/g).

The lower values of saturation magnetization and nanocrystaline ferrites pertaining to the

fact that the surface effect play vital role in supporting noncollinearity of magnetic moments on

their surface. Nanocrystaline particles consist of ferromagnetically aligned core spins and spin-glass

like surface layers .The disordered behavior in spin from the surface of the nanoparticles pushes to

modify the magnetic properties of these materials specially when surface/volume ratio is very large

[16].


18

CONCLUSIONS:

We have successfully synthesized single phase simple cubic spinal polycrystalline of MZN ferrite

and particles with an average crystalline size of 28 nm by sol-gel route. We observed from the

XRD, that the lattice parameter decreases with increasing cation substitution.

The prepared MZN ferrites exhibits’ superparamagnetic behavior at room temperature. The

Superparamagnetic properties of MZN ferrites are significant for biomedical applications. Such as

drug delivery, bioseperation and magnetic resonance imaging. From our research and findings, it

seems that the sol-gel autocombustion method may offer to synthesis other ferrite nanocrystals with

novel magnetic properties.

REFERENCES:

[1] Li, H. Wang, J. Magn, Magn. Mater. 309 (2007) 295.

[2] S. Y. Zhao, R. Qiao, X.L. Zhang, Y. S. Kang, I Phys. Chem. C111 (2007) 7875.

[3] S. Sun, H. Zeng, D. B. Robinson, S. Raoux, P. M. Rice, S.X. Wang, G. Li, J. Am. Chem. Soc.

126 (2004) 273.

[4] H. Deng. X, Li, Q. Peng, X. Wang, J. Chen, Y. Li, Angew. Chem. Int. Ed. 44 (2005) 2782.

[5] T. Hyeon, Y. Chung, J. Park, S. S. Lee, Y. W. Kim, B. H. Park, J. Phys. Chem. B 106 (2002)

6831.

[6] S. R. Ahmed, P. Kofinas, Macromolecules 35 (2002) 3338.

[7] L. Li, G. Li, R. L. Smith H. Inomata, Chem. Mater. 12 (2000) 3705.

[8] V. Berbenni, C.Milanese, G.Bruni, A.Marini, I.Pallecchi, Thermochim. Acta 447 (2006) 184.

[9] H.Yang, X.Zhang, C.Huang, W.Yang, G.Qiu, J.Phys. Chem. Solids 65 (2004) 1329.

[10] T.Meron, Y.Rosenberg, Y.Lereach, G.Markovich, J.Magn. Magn. Mater. 292 (2005) 11.

[11] J.Park, J.joo, S.G.Kwoon, Y.Jang, T.Hyeon, Angew. Chem. Int. Ed. 46 (2007) 4635.


19

Linear Power Amplifiers: Basic Considerations of Switched-Mode Assisted Amplifiers

N. V. Shiwarkar#, A. P. Bhat

&, K. G. Rewatkar

$

#Department of Electronics, Dr. Ambedkar College, Deeksha Bhoomi, Nagpur-22, India

&Department of Electronics, RTM Nagpur University, Nagpur-33, India

$Department of physics, Dr. Ambedkar College, Deeksha Bhoomi, Nagpur-22, India

Corresponding author: [email protected]

ABSTRACT:

The paper presents a combined high efficient amplifier system consisting of a linear

amplifier unit with a switched-mode(class D) current and voltage stage arranged in parallel. With

this topology the fundamental drawback of conventional linear power amplifiers - the high loss is

avoided. Compared to a pure class D (switching) amplifier the presented system needs no output

filter to reduce the switching frequency harmonics. This filter (usually of cascaded type) generally

try to avoide the transient response of the system and impairs the feedback loop design.

Furthermore, the low-frequency distortions of switching amplifiers caused by the inter system

response delay of the power transistors is avoided with the presented switched-mode assisted linear

amplifier system. This consideration as a master-slave system with a guiding linear amplifier and a

supporting class D slave unit. The work describes the operating principle of the system, analyzes the

fundamental relationships for the circuit design and presents simulation results with the help of

virtual lab.

Keywords: class D, harmonics, transient error, etc

INTRODUCTION

Conventional linear power amplifiers are replaced by switching (class D) amplifiers in an

increased quantity to overcome the essential drawback of linear amplifier systems[l]. The output

voltages of a class D amplifier imply a switching frequency component (harmonics) which may be

reduced by a proper filtering technique and circuitry. However, this filter - which has to be in

general of higher order type - reduces the dynamic response and increases the output impedance of

the whole amplifier system. Also, the interlock delay time of the usually applied bridge topologies, a

ripple of the DC supply voltage +V and the on-state voltages of the power semiconductor devices,

transistor and freewheeling diode may result in low-frequency distortion [2] which hardly can be

reduced by the described switching frequency output filter but has to be lowered by using a special

control loop design [3, 4]. A further problem of switching amplifiers is the possible occurrence of

harmonic frequency components which may result for a small signal-to switching-frequency ratio or

if a pulse width modulation strategy with variable switching frequency is applied. This harmonic

noise basically cannot be lowered by the output low pass filter because the frequency components

lie within the power bandwidth of the amplifier. A concept is proposed consisting of a parallel

arrangement of a class D switching system and a conventional linear amplifier stage.



20

Fig. 1 Simplified circuit diagram of a linear power amplifier

The output filter of the switching amplifier is reduced to a single coupling inductor

determining the switching frequency ripple. Although the linear amplifier can be considered as

active filter which compensates the switching frequency ripple and the modulation noise, the basic

idea of the proposed switched-mode assisted linear amplifier is that the linear amplifier acts as the

guiding master system whereas the task of the class D (slave) stage is to take over the current of the

linear stage (current dumping). In the ideal (stationary) case the linear power amplifier only has to

deliver the ripple of the class D stage which significantly reduces its power losses. Contrary to a

passive output filter of a conventional switching amplifier the linear amplifier of the proposed

concept also reduces low-frequency distortions and harmonic components. However, a very low

output impedance of the linear system part is importance to get a high noise rejection. This

performance is to be considered by an appropriate design of the linear amplifier circuitry and

feedback system. Furthermore, the switched mode assisted linear amplifier allows a significant

reduction as an idealized class D amplifier. Therefore, concerning the losses the proposed system

can be seen as intermediate solution between pure linear and pure class D power amplifiers.

SYSTEM CONTROL - CALCULATION OF POWER LOSSES

The guidance of the class D part is realized by a current controller whose reference value is

identical to the current through the load. Thus, only the control error and the ripple is delivered by

the linear stage. Instead of an explicit subtraction of reference value (load current i) and actual value

(class D stage output current is, ) the calculation of the controlling quantity can be done in an

implicit manner by direct measurement of the linear stage output current . As an alternative, a pulse

width modulator (PWM) with a superimposed linear current controller or other types of modulation

is to maintain the harmonics develop in the master and slave and reduced by the low pass filter

current controllers being well known from switched-mode power supplies (e.g., conductance

control) can be applied.

Fig.2 Circuit diagram of a switched-mode assisted linear power amplifier.


21

The pulse width modulator allows a switching frequency being constant which is, however,

of not essential significance for this application as stated before. An advantage of the hysteresis

controller is it’s inherent over modulation ability which yields a more efficient utilization of the DC

supply voltage *V. On the other side, PWM current controllers with their well defined switching

instants allow an easier extension of the class D stage to a parallel arrangement being operated in an

optimum phase shifted manner in order to reduce the total ripple current, or increase the effective

switching frequency, respectively. However, it should be mentioned that there exist solutions for

two hysteresis controlled converter branches (arranged in parallel) where a suboptimal phase shift

can be achieved in a very simple way. In the following, the losses of the linear amplifier stage shall

be calculated for the case that a hysteresis current controller with a constant tolerance band is

applied. It is assumed that the load current I and the output voltage V can be treated as constant

within the switching interval T or, that there exists a sufficient signal-to-switching frequency ratio,

respectively ( Fig.3). 'Switching Frequency The output voltage U (averaged within a pulse interval

T) is determined by the duty cycle. According to V, = Ldi,,/dt the switching frequency f, = 1/T can

be calculated.

Power Losses

The power losses of the linear stage depend on its operating mode, where one has to

distinguish between class A (linear amplifier with quiescent current eliminating crossover

distortions) and class B (without quiescent current) mode. the linear stage where it is assumed that

for class A mode the quiescent current is as small as possible, the class A mode losses are twice the

losses of the class B mode.

Frequency effect on the Amplifier Bandwidth.

The demand for low power losses implies a small ripple amplitude . However, for a defined

maximum switching frequency f, this would result in the usage of a high value of the inductance L.

On the other side, a higher value of L reduces the power bandwidth of class B of the switched-mode

current dumping stage. If we normalize gain bandwidth with respect to the value V/R (maximum

load current, resistive load EL = R assumed), kA = AI/(V/R), we receive for a class-B linear stage

(kA ... normalized ripple amplitude). The power bandwidth of the current dumping stage can be

defined as fB = R/ (2nL) .

The switching frequency to- bandwidth ratio is linked to the losses of the linear system. For

a given maximum switching frequency and a required power bandwidth of the whole amplifier the

current ripple (and therefore the power losses) is fixed. However, there are some possibilities to

overcome this fundamental limitation:

Usage of a higher supply voltage for the switching

Fig.3 Voltage and current waveforms of a switched-mode assisted linear power amplifier;


22

Fig. 4: switching technology module.

(a): switch stage output voltage; (b): output currents of the class D system and of the linear stage; (c)

transistor currents for class B mode of the linear amplifier part;

(2) splitting-up the current dumping stage in several parallel branches operated in a phase shifted

manner or application of a three-level topology

(3) Higher order type coupling impedance of the switching stage . It has to be noted that the

described effect only limits the power bandwidth of the current dumping stage and not of the whole

amplifier system whose dynamic response (especially the slew-rate) is determined by the linear

stage. MOSFET safe operating area a) and the power losses b) of conventional linear power

amplifiers and switched mode assisted linear (SMALA) amplifiers (both class B mode) for

sinusoidal output voltage and different load current displacement factors.

SIMULATION RESULTS

A prototype system of a switched-mode assisted amplifier system with the nominal values

V = 20V, R = 2.5R (resistive load ZL = R ; RMS value of the sinusoidal output voltage: 50V), fB =

l0 kHz, f = 200kHz shall be calculated briefly. The power losses of the proposed system are far

beneath the lsosses of conventional linear power amplifiers, especially for the case of non-resistive

loads (e.g., the losses of a conventional linear amplifier would be P = 1kW for M=l and Cosc=0.5).

However, it has to be admitted that the losses shown in Fig.4 for the switched mode assisted

amplifier do not include the losses of the switching stage. On the other side, the efficiency of

switched-mode bridge topologies usually lies above 95% so that the total losses of switched-mode

assisted amplifiers would not be increased significantly as compared to conventional linear

amplifiers. The current wave shapes of the simulated 1kW amplifier system are shown in Fig.5.

There, the pulse response demonstrates the limited slew-rate of the switched-mode current dumping

system. In this case the output current of the linear amplifier i,,, not only has to compensate the

ripple of the switching state but also has to take over the dynamic current peaks This effect results in

increased power losses of the linear stage.


23

LINEAR STAGE DESIGN

A very low magnitude Z of the high-frequency output impedance z of the linear stage is of

fundamental importance for a high input voltage signal-to-noise ratio (SNR) of the system because

the ripple current AI of the switching stage generates a noise voltage. Today, the output stages of

linear amplifiers usually are realized by using power MOSFET source followers [5]. The output

impedance of source followers is defined by the transconductance (g) of, e.g., the upper transistor

and is also influenced by the output impedance Ri of the driver stage in the upper frequency region.

Fig5 : three level NPC switching level

Fig. 6 : Output impedance of source followers.

In general, the transconductance of power MOSFETs is far too low to get an output

impedance in the desired level. This fact is not of primary significance because the effective output

impedance is reduced by the loop gain of the feedback system. For the described system we have to

adjust the loop gain to 50dB at 200kHz. A higher loop gain would allow to further increase the

SNR but would reduce the stability margin of the linear amplifier system. The frequency response

of the amplifier mainly is determined by that of the voltage booster stage because the output current

buffer usually shows a much higher bandwidth due to the application of MOSFETs and a high-

frequency driver stage using bipolar video transistors. Contrary to conventional linear power

amplifiers the frequency design of the voltage booster has to be performed not only regarding the

power bandwidth but also has to consider the switching frequency of the current dumping stage in

order to get the described reduction of the output impedance. Therefore, we use a symmetric wide-

band push pull differential amplifier arrangement with a relatively low gain of 10 which, on the

other side is high enough to use a conventional OP-AMP as feedback amplifier This OP-AMP is

used as a PI-controller to increase the loop gain in the region of lower frequencies and to enhance

the linearity of the system. A further improvement of the loop gain could be achieved by the well

known principle of splitting-up the voltage booster into a low frequency part with full output

voltage swing and a high-frequency small-signal path being arranged in parallel to increase the loop

gain in the switching frequency region [6].


24

ISOLATION OF SWITCH SIGNALS

The NPC topologies as shown would allow a SMALA to be built with equal power rating to

a full bridge design using an equal number of equal The hysteresis control strategy using a pair of

controllers retains the very simple sensing structure of the original. The drive of the outer

MOSFETS is also simple, requiring non-isolated drivers. The inner NPC MOSFETs do require

isolated gate drives. The low N channel device can be isolated using a level shifting boot strap

driver HVIC. Most logically, this would be a half bridge driver with independent channels, such as

the IR21xx family of devices [12], driving S3 and S4.

However, no equivalent device is available for the P channel devices, capable of level

shifting to a more negative voltage for device S2. Recent digital isolators using IC scale magnetic

coupling techniques from Analog Devices [13] and NVE corporation [14] have low propagation

delay, low power consumption, and excellent noise immunity.

CONCLUSIONS

It is observed that a simple extension of the hysteresis current control demonstrated in a previous

two level SMALA implementation is suitable for controlling a three level Neutral Point Clamped

(NPC) converter. The NPC topology allows the use of lower voltage switches and lower switching

frequencies to implement high power audio amplifiers. It has to be noted that concerning the output

impedance the realization of the output stage using bipolar power transistors would probably be a

better solution because of their higher trans-conductance as compared to MOSFETs.

ACKNOWLEDGEMENT

The author would thankful to the Department or Electronics RTMNU for providing Audio

Engineering details literature and alumni student working in practical world of audio Engineering

field.

REFERENCES

[1] Walker, G. R. “A Class B Switch-Mode Assisted Linear Amplifier”, Power Electronics, IEEE

Transactions on, Vol.18, No.6, pp.1278- 1285, Nov. 2003.

[2] G. B. Yundt, “Series or Parallel-Connected Composite Amplifiers,” IEEE Transactions on

Power Electronics, Vol PE-1, , pp 48-54. January 1986

[3] H. Ertl, J.W. Kolar and F.C. Zach, “Basic Considerations and Topologies of Switched- Mode

Assisted Linear Power Amplifiers,” IEEE Transactions on Industrial Electronics, Vol 44, No. pp.

116-123. 1997.

[4] N. S. Jung, N. I. Kim, and G. H. Cho, "A New High-Efficiency and Super-Fidelity Analog

Audio Amplifier with the aid of Digital Switching Amplifier: Class K Amplifier," presented at 29th

Annual IEEE Power Electronics Specialists Conference, 1998.

[5] R. A. R. van der Zee and A. J. M. van Tuijl, "A Power-Efficient Audio Amplifier Combining

Switching and Linear Techniques," IEEE Journal of Solid-State Circuits, vol. 34, no.7, pp. 985-991,

July 1999.


25

Synthesis Of ALMgFe12O19 Hexa Ferrite For Data Storage Application

P. M. Bodele#, A.P. Bhat

@, R.M. Singh

#, S. T. Chatterjee

# S. J. Dhoble

& K.G. Rewatkar

#

#Department of Physics, Dr. Ambedkar College, Nagpur-10 India @Department of Electronics, RTM Nagpur University, Nagpur-10 India

&Department of Physics, RTM Nagpur University, Nagpur-33 India


ABSTRACT

Manganese substituted Aluminum ferrite nanoparticals (AlxMg2xFe12-2xO19 with x = 0,0.5,1 )

were synthesized via sol-gel auto combustion route. X-ray diffraction (XRD), transmission electron

microscopy (TEM), scanning electron microscopy (SEM), and electron dispersive X-ray (EDX)

have been used to investigate the prepared Magnetic aluminum Nanocrystal (MAN). Magnetic

properties of the prepared samples have been detected by vibrating sample magnetometer (VSM), at

room temperature and the results of the prepared MZN exhibits a superparamagnetic (SPM)

behaviour. Their magnetic moment, saturation magnetization (Ms ), remanent magnetization (Mr,)

coercivity (Hc,) SQR, etc. are measured and studied. The temperature dependence of magnetization

as well as susceptibility is studied and discussed.

The electric properties of samples are also studied. The dc conductivity of the samples is

measured to know about their conduction mechanism. Activation energy is also determined to study

understand utility of samples in the industrial electronics. Basically, the samples are semiconducting

materials. By measuring their Seebeck coefficient and its temperature dependence, the type of

charge carrier is also confirmed.

.

Keyword: Magnetic measurements, Superparamagnetism

INTRODUCTION:

The development of civilization has been intimately linked with the ability of human beings

to work with materials. Indeed, the journey of this development was initiated in the Stone Age and

successively it got promoted in the copper and bronze, then Iron Age. This era of Nanoscience and

Nanotechnology of materials are the all new facets of such immense development. Magnetic

materials have a major contribution in the development of Nanotechnology and Nanoscience. The

recent researches in nano magnetic materials have enriched the applicability of nanotechnology in

the makings of new modern gadgets. In fact, the nanotechnology has developed the interest of end

users to purchase appliances and gadgets allied to Nanoscience and Nanotechnology.

The magnetic properties of materials have found to be changed drastically when the

material is transformed into nano scale. The recent researches in this field have confirmed that

materials with such structural, magnetic and electrical properties can easily be used for the

development of digital memories, cores, transducers, aero space devices, analyzers, cell phone

memories, etc. [D]. Besides, it is further cited that with further improvisation in such materials, they

can be used in telecommunication, satellite communication, computer technology, laser technology,

etc. When the size of the magnetic particle is reduced to nano scale, the multi-domain structure

generally turns into a single domain structure. Hence, the possible domain wall resonance is avoided

and the material can work at higher frequencies [F]. Moreover, the nanostructured materials have

the prospective to have better energy efficiency and storage.



26

This research work is intended to provide an updated study of nano scale magnetism for

data storage applications. Moreover, it emphasizes on the synthesis, characterization and

applications of nanoscaled magnetic materials especially Al-Mg substituted Hexaferrite

Nanoparticles. It not only deals with the physics and chemistry but also structural, morphological,

magnetic and electrical characteristics of such nano magnetic materials.

EXPERIMENTAL

Preparation of sample:

Powder of MAN ferrites particles were prepared by sol-gel auto combustion method. by Using

analytical grade chemical reagents of Mn(NO3)24H2O, Al(NO3)26H2O, and Fe(NO3)39H2O and

its stoichiometric proportions were first dissolved in deionized water. The mixture of solution was

heated at 800c till the complete mixture transformed in to gel. The gel of the solution which were

ignited and burnt by microwave oven on 600 watt for 7 minute to obtain ash powder. The powders

were annealed slowly at 8000c in a furnace for 4 hours after intermediate grinding.

Characterization Technique:

The phase identification and crystalline structural analysis of the thermally treated powder was

analyzed by X-ray diffraction (XRD, Bruker AXS D8 advance, Cu K radiation λ = 0.1540 nm).

The size and morphology of such prepared samples were characterized by scanning electron

microscopy. (SEM, Camca SU, SEM probe) and transmission electron microscopy (TEM, Phillips,

CM-200) for magnetic hysteresis loops were measured using a vibrating sample magnetometer

(VSM. Lakeshore 7410).

RESULTS AND DISCUSSION:

Fig.1. a & b) shows XRD pattern and broading of high intensity peak of AlxMg2xFe12-2xO19

b


27

The crystalline structures of MAN were characterized by XRD as shown in above fig.1 (a)

& (b). All the Bragg’s reflections have been indexed which confirmed the formation of simple

hexagonal structure in single phase without any impurity peak. The strongest reflection and

broadening of high intensity peak comes from the (107) planes as depicted by JCPDS card 84-1531

and 80-1197. which denote the spinel phase appearing at 30.070 & 35.110.The crystalline size were

calculated for (AlxMg2xFe12-2xO19 with X = 0.5,1) using high intensity peaks and using Scherer

formula i.e. dhkl = 0.9 /cos.The values are found to be 5nm and 15 nm.The lattice parameter for

Mn0.5Al0.5Fe12O19 and MnFe2O19 The values are found to be 5.4812 Å & 10.4699 Å. it was

found that the lattice parameter decreases with increasing cations substitution of Mn2+ due to

difference of ionic radius (ionic radius of Zn+2 is 1.35 Å & Mn+2 is1.40Å) and its atomic mass.

Fig .2 A Fig: SEM result of Al0.7Mg1.7Fe11.3O19 x =0.5,1 nanoparticles.

A typical TEM image of the prepared MAN nanocrystals has been shown in above fig.2. the

circular diffraction rings are clearly visible, indicating the nano crystalline nature of MAN. Most of

the such prepared magnetic nanocrystals are nearly spherical structure as per shown in TEM. Dark

regions are representative nanoparticles which are in agreement with the SEM findings below.

The morphogical studies of the Mn-Al ferrite powder was carried out using SEM. This type

of electron microscope is capable of producing high resolution images of a sample surface [13-14]

due to the manner in which the images are created. SEM images have a characteristic three

dimensional appearance and are useful for judging the surface structure of Mn-Al ferrite. It is found

that the powders were made up of particles with the size in the nano range as shown in fig.3. In

which the powder form of the solid sample was mounted on the conducting resin with dispersion

treatment, indicating that the almost spherical and homogeneous nanoparticles with the average size

of MZN are about 15 nm. This result is in agreement with the result of XRD and TEM analysis [17].

The chemical composition of such prepared ferrites samples was further confirmed by

energy-dispersive X-ray analysis (EDX). The result shows that Me2+/Fe3+ ratio is about 0.5 which

is in agreement with the expected stoichimetry in each case as shown in fig.3 EDX system are

attachment to SEM or TEM instrument where the imaging capability of the microscope identifies

the specimen of interest. The data generated by EDX analysis consist of spectra showing peak of

Mn, Fe, and O, corresponding to the elements making up the true composition of the sample being

analysed.The EDX technique is non-destructive and specimen of interest can be examined in

situation with little or no sample preparation.

100nm


28

Fig 3.SEM and EDX spectrum of the sample Mn Fe12O19

The magnetic properties of the prepared MZN were investigated with a VSM as shown in Fig.4.

Fig 4: Magnetization curve of nanocrystalline AlxMg2xFe12-2xO19 with X = 0.5,1. At room temp.

The magnetization curves measured at room temperature, from the curve the measured

magnetic saturation values are about 28 emu/g for Mn0.5Aln0.5Fe2O4 and 20 emu/g for

MnFe12O19. The corecivity of the as prepared magnetic nanocrystals at room temperature is

negligible, because in a nano size particals many single domains are uniformly magnetized with all

the spins aligned in the same direction. The magnetization will be in reversed spin rotation, since

there are no domain walls to move. I.e. this is the reason for the very high coercivity observed in

thin research module with reported values between 38 between 177 Gauss in small nano particles

[18, 20]. The superparamagnetic behaviour can be represented by hysteresis curve as shown in fig.4.

Superparamagnetism occurs in nanoferrites which are single domains i.e. composed of a single

magnetic domain. This is possible only when their diameter measures below 3-50 nm, depending on

the materials. Superparamagnetic materials do not retain any significant amount of magnetization in

the absence of externally applied magnetic field and thus do not form aggregates.

A curve between magnetization and applied field (20kG) at room temperature is shown in

fig.4. It shows typical superparamagnetic nature with no trace of hysteresis and coercivity 38G and

100nm

MnFe12O19 MnFe12O19


29

almost zero remanence. It also prominently showed non-attainment of saturation magnetization even

at 20KG.

The nonsaturation of M-H loop and the absence of hysteresis remanence and coercivity at

room temperature strongly suggests the presence of superparamagnetic behavior.The values of Ms

are higher in multidomain bulk ferrites (45 emu/g) [15], than the Mn-Al compounds represented in

the present work (Ms=28 emu/g).

The lower values of saturation magnetization and nanocrystaline ferrites pertaining to the fact that

the surface effect play vital role in supporting noncollinearity of magnetic moments on their surface.

Nanocrystaline particles consist of ferromagnetically aligned core spins and spin-glass like surface

layers .The disordered behavior in spin from the surface of the nanoparticles pushes to modify the

magnetic properties of these materials specially when surface/volume ratio is very large [16].

CONCLUSIONS

Doping effect on resistivity

The compositional dependence of resistivity (ρ) (at 393 K) for AlxMg2xFe12-2xO19

(0≤x≤1) (x = 0.00-0.10; y = 0.00-1.00) is presented in table 3.5. It is clear that the value of

resistivity increases from a value of 1.80 ×10 10 O cm for the undoped sample to 3.25 ×1010 O cm

for the sample with dopant level of Al = 0.06 and Mg =0.60, but decreases with further increase in

the dopant level. The observed variation can be explained in terms of site occupancy and nature of

the substituted ions. The substitution of Al 3+ to the Mg 2+ ion induces perturbation in both the

electron-density and symmetry around the 2b lattice site [15]. Lachevallier et al. [15] has reported

that among five lattice sites of Fe3+, the nearest neighbors of Mg ion in the Al-layer are 12k, 4f 2

and 2b (octahedral sites located in R block). 2b site is at a minimum distance of 0.340 nm to the 2d

site of Mg 2+ ions compared to the distance of 0.366 nm and 0.365 nm for 4f 2 and 12k sites.

Thus the presence of La near the octahedral site would not only change the separation between the

Fe 3+ ions but may also reduce the Fe obstruct electron transfer between Fe It has already been

reported that the Al 2+ 2+ -O-Fe and Fe2+ 3+3+ bond angle [30] which causes to ion pairs and

increases the resistivity. ions have a strong tendency to occupy the octahedral lattice sites (4f 2 ,

12k) [37], therefore, substitution by La-Ni ions partially replaces some of the Fe 3+ at the

octahedral site to consequently increase the resistive of Al-Mg hexaferrite. Enhancement of

resistivity is of significant 2+ 2+ 3+

Effect of applied field frequency on dielectric constant

The variation of dielectric constant (έ) for AL-Mg doped strontium-barium hexaferrite

series with respect to frequency from 100 Hz to 1 MHz are reported in figure 3.26. It has been

observed that έ, in general, show a decreasing trend with increasing applied frequency. For the

undoped strontium-barium hexaferrite, έ decreases continuously from 15.8 ×102 to 13.60 as the

frequency is increased from100 Hz to 1 MHz. However, the dispersion in the values of έ is fast at

low frequencies while it slows down at higher frequencies, in the studied range of frequency.


30

Figure 5: “Variation of dielectric constant (έ) with applied frequency

Effect of applied field frequency on dielectric loss tangent

The variation of dielectric loss tangent (tan d) with applied field frequency (from 100 Hz to

1 MHz) for the La-Ni doped strontium-barium hexaferrite series are presented in figure 3.30. It can

be noted that the value of tand decreases with increasing applied frequency. For the undoped

strontium-barium hexaferrite, tand decreases continuously from 4.5 to 0.10 as the frequency is

increased from 100 Hz to 1 MHz. However, the dispersion in the values of tan d is fast at low

frequencies while it slows down at higher frequencies, in the studied range of frequency. We have

successfully synthesized single phase simple cubic spinal polycrystalline of MAN ferrite and

particles with an average crystalline size of 5 nm and 16 nm by sol-gel route. We observed from the

XRD, that the lattice parameter decreases with increasing cation substitution.The prepared MAN

ferrites exhibits’ superparamagnetic behavior at room temperature. The Superparamagnetic

properties of MAN ferrites are significant for biomedical applications. Such as drug delivery,

bioseperation and magnetic resonance imaging. From our research and findings, it seems that the

sol-gel autocombustion method may offer to synthesis other ferrite nanocrystals with novel

magnetic properties.

The present research work is devoted to set an attempt for the development of Nano

sciences and technology in the field of magnetic materials. The magnetic materials have always

been remaining an issue of discussion in every decade of discovery of sciences. The effect of Al and

Mg substitution along with the doping of in AlxMg2xFe12-2xO19 has been investigated. The

hexagonal M-ferrite composition was successfully synthesized by sol-gel auto-combustion method.

The Al doping of ferrite helped in better densification. The Al-doped ferrite showed lowest

dielectric permittivity and dielectric loss. Also it showed highest permeability, lowest relative loss

factor and highest resistivity, respectively. The permeability was stable up to 1 MHz frequency.

According to all the data presented, it can be said that Al-doped would be a good material for multi-

layer ferrite chip data staorage

In the present investigation, a system of AlxMg2xFe12-2xO19 (0≤x≤1) is developed using

hybrid technique which is popularly known here as ‘Microwave Induced Sol-Gel Combustion

Route’. The synthesized M-type Calcium hexaferrite are found to exhibit a hexagonal symmetry,

P63/mmc or D46h (No. 194) with two formula units per unit cell.


31

The substitution with non-magnetic ions such as, Al results in low magnetic transition (Tc)

temperature. These compounds may act as a suitable substrate for thin epitaxial deposition of

hexaferrite films..

It is worth interesting to quote here that the nano hexaferrite particles synthesized in the

present investigation are observed to be having very small particle size of the order of 5.52 nm

earlier it is found to be 11.52 by shard sabale

ACKNOWLEDGMENT

The author would thankful to the Department of nanoscience and nanotechnology for effective help

and support during the project and UGC-DAE canter Indore for financial support and help

REFERENCES:

[1] F. Li, H. Wang, J. Magn, Magn. Mater. 309 (2007) 295.

[2] S. Y. Zhao, R. Qiao, X.L. Zhang, Y. S. Kang, I Phys. Chem. C111 (2007) 7875.

[3]S. Sun, H. Zeng, D. B. Robinson, S. Raoux, P. M. Rice, S.X. Wang, G. Li, J. Am. Chem. Soc.

126 (2004) 273.

[4] H. Deng. X, Li, Q. Peng, X. Wang, J. Chen, Y. Li, Angew. Chem. Int. Ed. 44 (2005) 2782.

[5] T. Hyeon, Y. Chung, J. Park, S. S. Lee, Y. W. Kim, B. H. Park, J. Phys. Chem. B 106 (2002)

6831.

[6] S. R. Ahmed, P. Kofinas, Macromolecules 35 (2002) 3338.

[7] L. Li, G. Li, R. L. Smith H. Inomata, Chem. Mater. 12 (2000) 3705.

[8] V. Berbenni, C.Milanese, G.Bruni, A.Marini, I.Pallecchi, Thermochim. Acta 447 (2006) 184.

[9] H.Yang, X.Zhang, C.Huang, W.Yang, G.Qiu, J.Phys. Chem. Solids 65 (2004) 1329.

[10] T.Meron, Y.Rosenberg, Y.Lereach, G.Markovich, J.Magn. Magn. Mater. 292 (2005) 11.

[11] J.Park, J.joo, S.G.Kwoon, Y.Jang, T.Hyeon, Angew. Chem. Int. Ed. 46 (2007) 4635.

[12] D.Caruntu, B.L.CCushing, G.Caruntu, C.J.O’Connor, Chem. Mater. 17 (2005) 3398.

[13] P.I.Slick, in Ferromagnetic materials,E.P.Wohlearth, Ed,Vol.2,196, North- Holland,

Amsterdam, The Netherland, (1980).

[14] B.S.Randhwa, J.Mater. Chem.10 (2000) 2847

[15] S.Gubbala, H . Nathani, K. Koizol, R.D.K.Misra, Physica B 348 (2004) 317.


32

Dielectric Properties of Microwave Absorbing Material Used In Computer RAM

A.P. Bhat1, S. J. Dhoble

2, K.G.Rewatkar

3

1Department of Electronics, RTM Nagpur University, Nagpur India-33 2Department of Physics, RTM Nagpur University, Nagpur India-33 3Department of Physics Dr. Ambedkar college , Nagpur India-22

[email protected], [email protected]

ABSTRACT:

This study was to produce sheets of microwave absorbing materials using conductive

polyaniline dispersed in a silicone rubber matrix and to characterize the electromagnetic properties

(absorption, transmission and reflection of electromagnetic energy; and electric permittivity and

magnetic permeability) of these sheets in the X-band (8 - 12 GHz). Two sheets were produced: one

2.80 mm thick and the other 4.39 mm thick. The thinner sheet absorbed incident microwave energy

more efficiently, attenuating up to 88% of the incident electromagnetic energy. Also, calculations

were performed in order to determine the electromagnetic parameters that optimize the absorbent

properties of these sheets. These calculations showed that these materials could be combined and

altered to produce absorbing materials with a wide range of absorbing characteristics.

Keywords: microwave absorbing material, conducting polyaniline, flexible sheets

INTRODUCTION

In general terms, it is possible to describe the interaction of an electromagnetic wave with

microwave absorbing materials (RAM's) as a phenomenon where the electromagnetic energy is

transformed into thermal energy. According to the principle of energy conservation, the

electromagnetic wave impinging on a material can be reflected, attenuated or transmitted through

the material. The response of the material to the wave depends on its intrinsic characteristics; the

absorption of energy by the material does not necessarily means that the material will heat up,

sometimes the opposite can occur, i. e., the material can cool down.

To produce a RAM, it is necessary to select a matrix material (insulating polymer, porous

substrate, etc.) that will act as a support for an energy-absorbing center. The absorbing center may

consist of, for example, a conducting polymer with good mechanical and chemical properties and

whose electrical conductivity can be modulated5. The behavior of conducting polymers illuminated

by electromagnetic radiation in the X-band (8 - 12 GHz) has been studied to understand how the

conductivity of these polymers affect the absorption of electromagnetic energy and how these

materials can be used in the production of RAM's.

The electric permittivity (ε) and magnetic permeability (μ) are parameters related to the

dielectric and magnetic properties of a material, and directly associated to their absorbing

characteristics. The relative permittivity and permeability are represented by Equations 1 and 2,

respectively; the values of these parameters are calculated from the experimental values of the

transmission and reflection coefficients of the material.




33

In these equations, the primed and double-primed symbols denote real and imaginary

components. When the material is lossy, the permittivity and permeability of are complex and some

of the incident electromagnetic energy is dissipated1. In the case of a magnetic material, losses are

produced by changes in the alignment and rotation of the magnetization spin. When an

electromagnetic wave illuminates a dielectric material, there is the formation of electric dipoles

which align in the direction of the applied field, and the dipole alignment is directly related to the

absorption of electromagnetic energy .The real component of the permittivity is associated with the

ability of the material to store energy, while the complex component is responsible for energy

dissipation. The use of polyaniline as an energy absorbing center allows the production of dielectric

RAM's with negligible magnetic permeability. Using a simple physical model, one can say that

dielectric materials behave as an electric circuit consisting of capacitors in parallel with resistors.

The knowledge of how to process materials and combine components, additives, and

polymer matrices are decisive factors in the final properties of the RAM21. Therefore, the aim of

this work was to measure the dielectric parameters of sheets produced by mixing polyaniline with

silicone rubber. The properties of the sheets were analyzed in the X-band in order to determine the

transmission, absorption and reflection coefficients of the material and also its electric permittivity

and magnetic permeability. Analytical calculations were performed to determine the absorbing

characteristics of the sheets for different thicknesses and when used in combination.

MATERIALS AND METHODS

Chemical procedures

The energy absorbing center (conductive polyaniline) of the RAM was processed first. This

polymer was produced chemically and in laboratory scale. The conductive form of polyaniline

(green color - emeraldine salt- powder form) was prepared from aniline and by the action of the

oxidizing agent ammonium peroxydisulfate in an acidic reaction medium (dodecylbenzenesulfonic

acid - DBSA). Following, the doped polyaniline powder was added to a matrix composed of either

one of two types of silicone rubber, L9000 and RTV630 (GE Silicones). The mixture was

homogenized by mechanical agitation, and the processed materials were poured into 30 × 30 cm

molds and dried at 70 °C overnight. Two different sheets were obtained; the sheet produced with

L9000 silicone rubber had a thickness of 2.80 mm, and the one produced with RTV630 silicone

rubber was 4.39 mm thick.

Electromagnetic evaluation

The electromagnetic properties of the sheets were analyzed using the waveguide technique

(closed system) in the frequency range 8 to 12 GHz (X-band). A rectangular wave guide was

coupled to a VSWR analyzer connected . The setup used for the measurements is shown in

Figure 1. Small samples (about 2 cm2) were cut from the sheets and inserted into the waveguide.

The complex electromagnetic parameters, (permittivity and permeability) were obtained from the

measured values The attenuation of the incident radiation by the RAM's was obtained from the


34

difference between the reflectivity of an aluminum plate (reference material, alloy 2024) and that of

the same aluminum plate covered with the RAM.

Analytical reflectivity of RAM's.

In the case of single-layer RAM's, a layer of absorbing material is placed in contact with a metal

plate (Figure 2). Changing the thickness of the absorbing materials and their electromagnetic

properties (permeability and permittivity) can vary the absorbing characteristics of the RAM.

The reflectivity of electromagnetic energy of a single-layer RAM as function of frequency can be

calculated using the following equation:

In the above equations, μ and ε are, respectively, the complex permeability and permittivity

of the absorbing material, k is the wave number, f is the frequency of the incident electromagnetic

wave, c is the speed of light in vacuum, and d is the thickness of the absorbing layer. Both the

permeability and permittivity may vary with frequency.

Two or more layers of absorbing material can be stacked (Figure 3) in order to improve the overall

performance of the RAM.


35

The reflectivity of electromagnetic energy by a two-layer RAM can be calculated using the

following equation10:


In Figure 4 are shown the results derived from measurements (reflected, transmitted and

absorbed electromagnetic energy) as a function of frequency for the two single-layer RAM's

produced in this study. Figures 4 a andb show that both materials behave in a similar way; the

absorbed, reflected and transmitted energies vary approximately linearly with frequency. Also, for

both materials, the value of absorbed energy increased by about 10% with frequency in the

frequency range of the measurements. The maximum energy absorption, which was measured at

8 GHz, was 18.5 and 16.2% for the materials with 2.80 and 4.39 mm respectively, showing that the

thinner material had better absorbing properties. When the reflectivity of these materials were

measured using an aluminum back plate (a situation similar to their use in the real world, i.e.,

RAM's are used to coat metallic objects) the 2.80 mm thick material absorbed 88% of the incident

energy at 8 GHz whereas the 4.39 mm thick material absorbed 71% of the incident energy this

frequency. Lower values of absorption were obtained for higher frequencies. The behavior of both

materials clearly indicates their potential for the production of RAM's, especially for civilian

applications. The electromagnetic properties of the absorbing of these materials are shown in

Figure 5.

These differences in behavior shown in Figure 5a and b are due to the different matrix

compounds (silicon rubbers) used, since the absorbing center (conducting polyaniline) was the same

for both materials. For the silicone rubber L9000 (Figure 5a), the real and imaginary values of the

relative permittivity vary from 6.5 to 5.5 and from 2.1 to 1.85; for the silicone rubber

RTV630 (Figure 5b) the real and imaginary relative permittivity vary little with frequency and their

average values are about 3.5 and 5.0, respectively. As expected, since the materials were produced

using dielectric components, the values of the real and imaginary magnetic relative permeability

http://www.scielo.br/img/revistas/mr/v13n2/13f04f.gif



36

were approximately 1 and 0, respectively, and did not show any major variation with respect to

frequency.

By definition, the real permittivity values are equal or larger than one. In an ideal material

with zero dielectric loss, the real and imaginary permittivities are equal to 1 and 0, respectively; in

this situation the material does not store (ε' = 1) nor dissipate (ε" = 0) energy. The larger the value of

the imaginary component of permittivity the larger is the loss in the material. A material with low

dielectric loss can store energy, but will not dissipate the stored energy. On the other hand, a

material with high dielectric loss does not store energy efficiently and part of the energy of the

incident wave is converted into heat within the material23.

Based on this information and on the results of Figures 5a and b one is led to the conclusion

that the 2.80 mm thick material (silicone matrix L9000) is indeed has the best absorbing properties

of the two RAM's produced in this study, as is evidenced by the results depicted in Figures 4a and b.

Based on the experimental data (permittivity and permeability) and on Equation 3, it is

possible to optimize the thickness of the RAM's with respect to the absorption of energy and its

intended use. Figures 6a and b show how changes in the thickness affect the ability of the RAM's to

absorb energy. The curves in these figures were obtained assuming that the RAM's were used to

coat a flat metallic plate (Figure 2). Another interesting result shown in these figures is the

displacement of resonance peak (maximum absorption) as a function of the thickness; note,

however, that the absorption amplitude does not vary significantly. These calculations also show the

RAM produced with the silicone rubber L9000 absorb electromagnetic energy more efficiently.

The single-layer materials developed in this study can be combined into multi-layer

materials to produce RAM's with different absorbing properties. Using the experimental data

collected on the single-layer materials, it is possible to simulate the behavior of two-layer RAM's

using Equation 5. Figure 7 shows the results of simulations when these materials are combined in

different configurations to produce a material with a total thickness of 10 mm. In these curves,

Z1 and Z2 refer to absorbing materials with the same electromagnetic properties of the materials

prepared with silicone rubber type L9000 and RTC6300, respectively. The results in Figure 7a were

obtained using 2 and 8 mm thick layers; in Figure 7b, both layers were 5 mm thick. It is interesting

to observe that the order in which these materials are stacked plays an important role in determining

the final properties of the RAM, affecting the amplitude and the position of the resonance peak.

CONCLUSION

The attenuation pattern of electromagnetic energy by the absorbing materials suggests that

the electrical conductivity of these materials is related to the quantity of absorbing centers

(conducting polyaniline) and type of polymer matrix (silicone rubber), which modify the impedance

of absorbing materials. In absorbing materials, a large fraction of the incident energy must be

attenuated, which is a consequence of the equilibrium between electric conductivity and electric

losses.

The materials produced with conductive polyaniline dispersed in a silicone matrix

attenuated the incident radiation up to about 88%, demonstrating that these materials can be used as

absorbers of electromagnetic radiation. Also, the analytical calculations demonstrated the

importance of optimization tools to produce absorbing materials with the required properties, since

variations in the thickness or the combinations of materials with different properties can improve the

absorbing qualities of the final material.





37

Another important characteristic of the materials produced using conducting polyaniline and

silicone rubbers is their low density compared with conventional absorbers based on ferrites

(absorption 10 dB), with densities ranging from 4 to 5 g.cm-3.

REFERENCES

[1]. Schleher DC. Electronic warfare in the information age. London: Artech House; 1999

[2]. Folgueras LC and Rezende MC. Hybrid multilayer structures for use as microwave absorbing

material. In: Proceedings of the IEEE 2007/MTT-S International Microwave and Optoelectronics

Conference; 2007; Salvador, Brazil. Salvador: IMOC; 2007. p. 483-487.

[3]. Kovetz A. Electromagnetic Theory. New York: Oxford; 2000.

[4]. Knott EF, Shaeffer JF and Tuley MT. Radar Cross Section. 2 ed. Norwood: Artech House;

1993.

[5]. Folgueras LC and Rezende MC. Multilayer radar absorbing material processing by using

polymeric nonwoven and conducting polymer. Material Research. 2008; 11(3):245-249.

[6]. Hourquebie P and Olmedo L. Influence of structural parameters of conducting polymers on

their microwave properties. Synthetic Metals. 1994; 65(1):19-26.

[7]. Faez R, Martin IM, Paoli MA and Rezende MC. Microwave properties of EPDM/PAni-DBSA

blends. Synthetic Metals. 2001; 119(1):435-436.

[8]. Faez R, Rezende MC, Martin IM and Paoli MA. Polímeroscondutoresintrínsecos e

seupotencialemblindagem de radiaçõeseletromagnéticas. Polímeros: Ciência e Tecnologia.

2000;.

[9]. Bhadra S, Khastgir D, Singha NK and Lee JH. Progress in preparation, processing and

applications of polyaniline. Progress in Polymer Science. 2009; 34:783-810.

[10]. Balanis CA. Advanced Engineering Electromagnetics. New York: John Wiley and Sons; 1989.

[11]. Lee SM. International Encyclopedia of Composites. New York: VCH Publishers; 1991.

[12]. Clark DE, Diane CF, Stephen JO and Richards S. Microwaves: Theory and Application in

Materials Processing III. Westerville: The American Ceramic Society; 1995.


38

Gsm Based Heart Monitoring System for Pre-Mature Babies

A.P.Bhat., S. P. Mesharam., K. K. Dhawad., A.A. Ballal

Department of Electronic and computer science RTM Nagpur University Nagpur-33

Department of Applied Elelctronics, LAD College of Women’s RTMNU Nagpur,

[email protected]

ABSTRACT

Application of engineering and technology has proved its significance in the field of

biomedical. It not only made doctors more efficient but also helped them in improving total process

of medication. The Patient monitoring system is also a new step in the automation of supervision for

doctors. The Patient monitoring system for doctors provides solution for this. It continuously

provides following information to doctors.

1. Heart pulse rate

2. Temperature

3. Body Position

As used in hospital the same system can be used for a person who is not under the continuous

observation of doctor. Also this project to aim towards as the monitoring tool for premature baby

place in Incubator. The normal body temperature of a healthy and resting human being is stated to

be at98.4°For 37°C. Though the body temperature measured on an individual can vary, a

healthy human body can maintain a fairly consistent body temperature that is around the mark of

37.0°C.An indication is sent to the doctor when the pulse rate starts fluctuating just above or below

ideal pulse rate which is 72 pulse/min., for a normal human body. Body positioning plays a

significant role in determining the pressure on heart. Since GSM endows its users with a voice and

data channel and the possibility of sending an indication to other terminals. Thus GSM find its use

and adaptability in our project.

Keywords:- GSM, Premautar baby, biomedical parameter, communication protocol, ISM Band

INTRODUCTION

Cases of heart attacks and deaths due to lack of help are increasing. For this purpose personal

monitoring are best solution. For heart patients this kit gives indication to their doctors and they

immediately get medical help. Whenever beat rate of person exceeds more than 72pulse/min.,

doctor get immediate indication and help will be sent as fast as can. Cardiovascular diseases are

often very critical and serious condition, the change is so rapid, the one attack can bring about great

suffering to patients, and even lead to syncope or sudden death. Especially coronary heart disease,

cardiomyopathy, and arrhythmia history, family history of sudden cardiac death, heart

transplantation and other medical conditions, history, the disease has a sudden, random, high rate

characteristics of sudden death, usually after the acute onset of symptoms within 1 hour may cause

death and malignant ventricular fibrillation within 12 minutes and even cause sudden death in

patients suffering from serious heart disease in patients with the above mentioned is attack patients.

Drawbacks of present electrical method and the wireless system:

The current heart rate monitoring system uses a heavy and bulky setup at both ends i.e. at the

patient’s as well as at the doctor’s. This in turn causes convenience problems for the patient and any



39

M

C

U GSM

BEEP

AMPLIFIRE &

FILTER

SENSOR

CKT

LCD

defect occurring at any stage may result in loss of information which may result in improper

diagnosis.

Need of system:

The present monitor puts forward a novel system that benefits from GSM module and telephony

standard widespread technology. This design adds to the traditional capabilities, the attractive

features of real time processing and possibility of monitoring the patient’s heart anywhere,

anytime. Apart from traditional typical capabilities, the new system presents additional features,

both in automatic analysis and in the communications interface (GSM transmission)

BLOCK DIAGRAM OF GSM BASED SYSTEM

Figure 1: Block diagram of HRM System

DESCRIPTION OF BLOCK DIAGRAM:

The above figure shows the block diagram of GSM based HRM(Heart rate monitoring )

system. Slight fluctuation in the normal heart rate , body temperature and change in body position

of patient will be sensed by the heart sensor , temperature sensor and posture detector respectively,

attached to the index finger. It will forward data to the microcontroller where it will be compared

with the normal value of body temperature and heart rate. Depending upon the parameters

considered by monitor, if it finds any parameter disturbed then the result is send to the doctor and he

may immediately take the necessary action. Thus without wasting the time patient can be treated

whereas sending the report can be done using GSM. The device will compare the three parameters

with the ideal parameters, if some fluctuations are noticed, the SMS is immediately sent to the

doctor. This message may be in the form of beeps to indicate the doctor. The system comprises an

implantable medical device that includes a sensor operable to produce an electrical signal

representative of heart sounds, a sensor interface circuit coupled to the sensor to produce a heart

sound signal, and a controller circuit coupled to the sensor interface circuit. The sounds are

associated with mechanical activity of patient’s heart and the controller circuit is operable to detect

a posture of the patient from a heart sound signal electrical signal representative of heart sounds, a

sensor interface circuit coupled to the sensor to produce a heart sound signal, and a controller circuit

coupled to the sensor interface circuit. The heart sounds are associated with mechanical activity of

patient’s heart and the controller circuit is operable to detect a posture of the patient from a heart


40

sound signal GSM based heart rate monitoring and the display system is a portable and a best

replacement for the old model stethoscope, which is less efficient. It is a combination of a

instrumentation based heart rate monitor interface with a GSM module to transmit the heart rate of

patient to a remote location.

The functioning of this device is based on the truth that the blood circulates for every

heartbeat that can be sensed by instrumentation amplifier and sensing pad. Depending upon the rate

of circulation of blood the heart beat per minute is calculated. This calculated value is

communicated to the person through a GSM modem interfaced to it.

CIRCUIT DIAGRAM

Patient’s heart and the controller circuit is operable to detect a posture of the patient from a

heart sound signal electrical signal representative of heart sounds, a sensor interface circuit coupled

to the sensor to produce a heart sound signal, and a controller circuit coupled to the Sensor interface

circuit. The heart sounds are associated with mechanical activity of patient’s heart and the controller

circuit is operable to detect a posture of the patient from a heart sound signal

Figure 2: - sensor circuit Figure3: microcontroller circuitry.

WORKING

The above circuit shows the working of the heart rate monitoring system using GSM.

Here at pin no. 1, 9 and 10 are connected to 3 capacitors in parallel. A crystal oscillator is placed

between pin no. 9 and10.Pin no.7, 20 and 21 are connected to +5v. The capacitors are connected to

GND at one terminal, also pin no. 8 and 22 also to ground. The output of the microcontroller is

given at PORT C from PC0 to PC3 as LM35, Heart Beat Sensor, to ADXL X axis from Pin no. 23

to 26. The RXD and TXD of microcontroller is connected to TXD and RXD of mobile. A voltage

regulator is used to regulate the voltage which is supplied form a 9v battery and gives an output of

5v. This gives the entire working of heart rate monitoring system using GSM.

Components of block diagram:

HEART SENSOR

LM35

POSTURE DETECTOR

MICROCONTROLLER ATMEGA8

GSM MODEM


41

Heart sensor:

The heart sounds are the noises a physician listens by using a stethoscope over the heart. They are

the noises of the heart valves shutting. These noises areHeart beat is sensed by using a high gain

amplifier using AD624Ad. The sensor is placed in such way that the differential instrumentation

amplifier transistor be used. The skin may be transmitted or low amplitude signal for detection. The

very small changes in in transmittance caused by the varying blood content of human tissue are

almost invisible. Various noise sources may produce disturbance signals with amplitudes equal or

even higher than the amplitude of the pulse signal. Valid pulse measurement therefore requires

extensive preprocessing of the raw signal.

The new signal processing approach presented here combines analog and digital signal processing

in a way that both parts can be kept simple but in combination are very effective in suppressing

disturbance signals. The setup described here uses of a siganal pickup sensor for transmitted for

sensing the signals and a instrumentation amplifier as detector. With only slight changes in the

preamplifier circuit the same hardware and software could be used with other detection concepts.

The nose problem of the circuit is solve using following circuit with the preamplifier and fixed band

filter

Figure 4:- sensing point and signal condition block.

The filter/amplifier circuit is a standard design and is documented in many sources (e.g. 0). The

signal from the IR sensor is very weak where the voltage is just around 50µV, containing a

significant noise level. The signal is affected by interference caused resulted from movement of

artefacts like rings and mains 50Hz. It is known that the standard ECG signals has the frequency

component in the range of 0.05-200H.if the filtered range is 0-50H, the signals dose not

suffering significant loss of quality or the information within the signal. The filtering possess is

necessary to block the higher frequency noise component present in the signal.

Features:

Heart beat indication by LED

Instant output digital signal

Easily available and less costly

Compact size

Working voltage +5v DC


42

LM35:

The LM35 series are precision integrated- circuit temperature sensors, whose output voltage is

linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has anadvantage

over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large

constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not

require any external calibration or trimming to provide typical accuracies of ±1⁄4°C at room

temperature and ±3⁄4°C over a full −55 to +150°C temperature range. Low cost is assured by

trimming and calibration at the wafer level. The LM35’s low output impedance, linear output,

and precise inherent calibration make interfacing to readout or control circuitry especially easy. It

can be used with single power supplies, or with plus and minus supplies. As it draws only 60 μA

from its supply, it has very low self- heating, less than 0.1°C in still air. The LM35 is rated to

operate over a −55° to +150°C temperature range, while the LM35C is rated for a −40° to +110°C

range (−10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46

transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic

TO-92transistor package. The LM35D is also available in an 8-lead surface mount small outline

package and a plastic TO- 220 pa

Features:

Calibrated directly in ° Celsius (Centigrade)

Linear + 10.0 mV/°C scale factor

0.5°C accuracy guarantee-able (at +25°C)

Rated for full −55° to +150°C range

Suitable for remote applications

Low cost due to wafer-level trimming

Operates from 4 to 30 volts

Less than 60 μA current drain

Low self-heating, 0.08°C in still air

Nonlinearity only ±1⁄4°C typical

Low impedance output, 0.1 W for 1 mA load

Posture detector using sensor:

The motivation to include posture detector in this project comes from the basic need to support the

independent living of elder people and smart personal alarm system to detect deviation in health

status. The earlier the fall is reported, the lower is the rate of morbidity-mortality. The use of

automatic fall detector decreases the fear of falling and improves the independence and the security.

It increases the quality of life of elder people. The measurement of movement of body is made with

the help of tilt sensor and accelerometer and the processing and analysis of movement is done with

the help of microcontroller. The graph shows the percentage of falling people which is likely to

increase every year. Patient’s posture is an important factor in the diagnosis of certain medical

disorders and may also be used to enhance therapy delivery. Posture detection involves determining

an orientation of the patient’s body, such as determining if the patient is in vertical position ,

determining if the patient in in a horizontal position (lying on the back, lying on the stomach, lying

on left or right side),or determining if the patient’s body is tilted to right, left, forward or backward.


43

Posture detection in accordance with embodiments describe herein may additionally include

determining an angle of tilt of patient’s body. Posture information may be tracked over time, stored,

and /or correlated. Information about patient posture may be evaluated with respect to the detection

of various disorders to determine if an association between patient’s postures and a particular

disorder is present. The posture of patient’s body, such as the inclination of the upper torso, may

be linked to various medical disorders, including disorders affecting the respiratory and/or

cardiovascular systems. Tracking patient’s posture over time can be used to assess the general well-

being of a patient.

The consequences of falling lead to sudden death or may lead to severe harm to the person which

can be listed to a few as follows:

30% of home-dwelling elderly (65+) fall each year

0-20% of elderly people fall recurrently(at least twice within 6 month)

Mean incidence of fall is about 650/1000 person years

860 older people (65+) died because of fall- related accidents

Microcontroller ATMEGA8

The ATmega8 features a 10-bit by executing powerful instructions in a single clock cycle;

the ATMEGA achieves throughputs up to 16 MIPS. The ATMEGA is a low-power CMOS 8-bit

microcontroller based on the AVR RISC architecture, approaching 1MIPS per MHz, allowing the

system designer to optimize power consumption verses processing speed. This microcontroller

works in 5 different modes which enhance its working.

The ATMEGA8 AVR is supported with a full suite of program and system development tools,

including C compilers, macro assemblers, program debugger/stimulator, in-circuit emulators, and

evolution kits.

GSM MODEM:

GSM (Global System for Mobile Communication; originally from Group Special

Mobile) is the most popular standard for mobile telephony systems in the world. The

implemented prototype utilizes a GSM modem. This modem can be operated by the micro-

controller by means of straight forward Hayes (ATA) commands, which follow the ETSI GSM 300

standard [9]. Using those commands, all functionality provided by a GSM terminal (voice, data,

SMS) can be exploited. It is easily available in the market and weighing less than 20gm, which is

smaller than a matchbox, thus allowing system reduction and integration. A separate module can be

demolished; especially suitable for the use of multiple machines at the same time. It is used to avoid

high communication costs to be incurred in a month; it sends in clusters which can be sent

automatically to a large number of goals the same information.

The purpose of this project is to measure the heartbeat and send the heart beat monitoring

and display system is the portable and best replacement for the old model stethoscope, which is less

efficient. It consist detector sensor based heart rate monitor interfaced with a GSM module to

transmit the heart rate of the patient to transmit the heart rate of the patient to a remote location.

Depending upon the rate of circulation of blood, the heart rate per minute is calculated. This

Calculated value is communicated to a doctor through a GSM modem interfaced to it. Based on

several scenarios we present the functionality of a prototype we are building. The application is

capable of monitoring the health of high risk cardiac patients. The smart phone application analyses


44

in real-time sensor and environmental data and can automatically alert the ambulance and pre-

assigned caregivers when a heart patient is in danger. It also transmits sensor data to a healthcare

center for remote monitoring by nurse or cardiologists. The system can be personalized and

rehabilitation programs can neither monitor the progress of a patient. GSM modem is

interfaced with the microcontroller with the help of ATA commands.

Feature of GSM:

Maximum transmission speed of 9.6Kbps

Coverage of 98% of the territory

SMS of around 150 characters

Cheap and are easily available

Support tri band mobile phones, a feature available with very few modules.

ADVANTAGES:

It is a small, low cost and a portable device which can be carried easily. Provides continuous

monitoring.

The mobility in the monitoring process is continuous. It is extremely useful to increase your

exercise level in a graded and careful manner in order to avoid injuries, overexertion, and excessive

stress on the cardiovascular system.

Using a heart rate monitor is an ideal method of assessing one’s cardiovascular condition, and

gauging the level of intensity of the exercise session.

The heart rate monitor is useful for individuals who have been advised not to exercise above a

certain heart rate because the heart rate can be monitored continuously.

It allows an athlete to be more in touch with your body and your heart rate.

An added bonus is that heart rate monitors not only supervises a person’s heart rate, it also

keeps track of the calories burned that you can monitor your improvement over time.

Heart rate monitor is an ideal is an ideal method in assessing your cardiovascular condition.

Disadvantages:

Using this for long durations could lead to soreness and chafing of the skin.

A sudden failure of network may hamper the working of the system.

APPLICATIONS:

We can also observe the ECG report of a patient on the cell phone with the help of this system.

By programming the GSM module with proper commands, the doctor as well as the family

members will be informed simultaneously about the fluctuations in patient’s condition. We can

also observe the ECG report of a patient on the cell phone with the help of this system. For keeping

track of cardiac system of an athlete to give him proper training. In defense areas, where the

remote location of a soldier can be determined. In hospitals, medical colleges, laboratories.

Future Aspects:

The system can be further improved in several aspects. Once the system requirement have been

clearly defined, the hardware can be optimized, especially regarding its size, weight and

consumption.


45

Together with clinical analyses, the protocols to optimize the system performance should be

established. New technology such as Bluetooth, GPRS and UMTS could also enhance the

performance of the final product.

Furthermore works in progress to develop and integrate a real time multichannel mobile

telemedicine system capable of simultaneously transmitting medical data such as ECG, Non

Invasive Blood Pressure(NIBP) and SpO2 applying Bluetooth and GPRS technologies could be

done, to make the system more flexible.

RESULTS & CONCLUSION:

Gender

Age

HR on display

97

HR on scope

96

Error %

1.03 Male 22 83 81 2.41

Male 20 78 78 0

Male 22 90 87 3.33

Male 20 80 79 1.25

Female 22 77 77 0

Female 22 104 103 0.96

Female 19 75 75 0

Female 20 69 71 2.81

Female 22 83 85 2.35

Figure 5:- wave shape on CRO Chart 1:- Wave shape of ECG

CONCLUSION

Wireless intelligent heart beat rate monitoring system have made possible a new generation of

noninvasive, unobtrusive personal medical monitors applicable during abnormal activities. There


46

are many ongoing researches on heart monitoring system using GSM and the main purpose behind

these researches is to make this system more compact, easily available at affordable price and to

include as many parameters as possible required for heart rate monitoring. New technologies could

also enhance the performance of the final project.

ACKNOWLEDGEMENT

The author would like to thank the staff of the Electronics’ and software simulation lab, LAD &

SRP College for their valuable assistance. Also the academic staff of Department of Applied

Electronics and software technology for continuous help and support.

REFERENCES

[1] Department of Computer Science and Engineering, Khulna University of Engineering &

Technology (KUET), Khulna 9203, Bangladesh, 2010.

[2] S.Allender, V.Peto, P.Scarborough, A.Boxer and M.Rayner ,Coronary heart disease

statistics, , British Health Promotion Research Group, Heart Foundation Department of public

health, University of Oxford, 2007.

[3] Mohamed Fezari, Mounir Bousbia-Salah, and Mouldi Bedda, “Microcontroller Based Heart

Rate Monitor”, The International Arab Journal of Information Technology, Vol. 5, No. 4,

2008.

[4] Dogan Ibrahim, Kadri Buruncuk,“Hear Rate Measurement from the Finger using a

low cost Microcontroller” ttp://www.emo.org.tr/ekler/a568a2a 8c19a31_ek.pdf

[5] Boashash, B., “Time-Frequency Signal Analysis and Processing: A Comprehensive

Reference”, Oxford: Elsevier Science, 2003.

[6] R. Fensli, "A Wireless ECG System for Continuous Event Recording and Communication to a

Clinical Alarm Station", Proc of the 26th Annual International Conference of the IEEE EMBS,

2004.

[7] http://www.brianmac.co.uk/maxhr.htm, Accessed on 02/09/2011

http://www.brianmac.co.uk/maxhr.htm


47

Microcontroller Based Heart Rate Monitor using Fingertip Sensors

A.P. Bhat1 , S. J.Dhoble

2 , K. G. Rewatkar

3

1Department of Electronics, RTM Nagpur University, Nagpur India-33 2Department of Physics, RTM Nagpur University, Nagpur India-33

3Department of Physics Dr. Ambedkar college, Nagpur India-10

[email protected]

ABSTRACT:

This paper presents the design and development of a microcontroller based heart rate

monitor using fingertip sensor. The device uses the optical technology to detect the flow of blood

through the finger and offers the advantage of portability over tape-based recording systems. The

important feature of this research is the use of Discrete Fourier Transforms to analyse the ECG

signal in order to measure the heart rate. Evaluation of the device on real signals shows accuracy in

heart rate estimation, even under intense physical activity. The performance of HRM device was

compared with ECG signal represented on an oscilloscope and manual pulse measurement of

heartbeat, giving excellent results. Our proposed Heart Rate Measuring (HRM) device is

economical and user friendly.

Keywords: Heart rate monitor; Fingertip sensor; Microcontrollers; Fourier transform

INTRODUTION

Heart rate is the number of heartbeats per unit of time, typically expressed as beats per

minute (bpm). Heart rate can vary, as the bodies need to absorb oxygen and excrete carbon dioxide

changes during exercise or sleep. Medical professionals to assist in the diagnosis and tracking of

medical conditions use the measurement of heart rate. Individuals, such as athletes, who are

interested in monitoring their heart rate to acquire maximum efficiency, also use it. The wave

interval is the inverse of the heart rate 0.

Changes in lifestyle and unhealthy eating habits have resulted in a dramatic increase in

incidents of heart and vascular diseases. Furthermore, heart problems are being increasingly

diagnosed on younger patients. Worldwide, Coronary heart disease is now the leading cause of

death 0. Thus, the medical community welcomes any improvements in the diagnosis and treatment

tools. In a clinical environment, heart rate is measured under controlled conditions like blood

measurement, heart beat measurement, and Electrocardiogram (ECG) 0. However, there is a great

need that patients are able to measure the heart rate in the home environment as well 0. A heart rate

monitor (HRM) is a simple device that takes a sample of the heartbeat signal and computes the bpm

so that the information can easily be used to track heart conditions. The HRM devices employ

electrical and optical methods as means of detecting and acquiring heart signals.

Heartbeat rate is one of the very important parameters of the cardiovascular system. The

heart rate of a healthy adult at rest is around 72 bpm. Athletes normally have lower heart rates than

less active people. Babies have a much higher heart rate at around 120 bpm, while older children

have heart rates at around 90 bpm. The heart rate rises gradually during exercises and returns

slowly to the rest value after exercise. The rate at which the pulse returns to normal is an indication

of the fitness of the person. Lower than normal heart rates is usually an indication of a condition

known as bradycardia, while higher than normal heart rates are known as tachycardia. Most HRM

devices use a design where the signal is acquired from the subject and a filtering function is applied



48

M C U Atmega 16

Bu

zze

r

GS

M

Signal Conditioning

Keyp

ad

LC

D

T

x

R

x

to remove the high order harmonics and noise from the signal. This is then followed by a hardware

or software that uses a zero crossing algorithms to count the number of beats during a given time

interval. The zero-crossing algorithm may lead to false readings caused by local noise that may

result in multiple locals zero crossings.

In this paper, we eliminated the zero-crossing problems by the use of Fourier Transform of

the digitized signal. This is a reliable technique that guarantees the automatic filtering of any

transient noise in the signal. The design and development of a low powered HRM device is

presented. The device provides an accurate reading of the heart rate using optical technology. We

incorporated the optical technology using standard infrared Light Emitting Diode (LED) and photo-

sensor to measure the heart rate using the index finger. A microcontroller is programmed to acquire

the signal using its embedded analogue to digital converter, ADC, and use the readings to compute

the heart rate; eventually, the reading is digitally displayed on a LCD. In case the HRM device is

used in a continuous monitoring mode 0, the device alert the medical professional or the person

accompanying of the patient, if the heart rate falls outside a given range. A local audible alarm is

also provided. The rest of the paper provides a discussion on the system overview; describes the full

description of the HRM device and lists the experimental results.

SYSTEM HARDWARE

The proposed HRM device is intended to have the following features:

− The system provides an optical mechanism to detect physical changes.

− The system supports a keypad to allow the user to enter information like name, age and

telephone number.

− The device is connected to an SMS modem to allow the transmission of an alert text message to

a medical profession

− The system provides a LCD screen to output the measured heartbeat rate.

− The device would provide an audible warning tone.

Figure 1. Diagram of the proposed device.

The system consists of an infra red (IR) LED as transmitter and an IR phototransistor as a receiver

that acts as a fingertip sensor


49

Fingertip Sensor

The sensor consists of an IR light emitting diode transmitter and an IR photo detector acting as the

receiver. The IR light passes through the tissues. Variations in the volume of blood within the finger

modulate the amount of light incident on the IR detector. Two practical configurations could be

implemented to achieve this function. In the first configuration, the finger can be placed between the

transmitter and the receiver as shown in Fig. 2. In the second design, both the IR transmitter and

receiver could be placed on the same plane and the finger would function as a reflector of the

incident light instead. The IR receiver monitors the reflected signal in this case. The IR filter of the

phototransistor reduces interference from the mains 50Hz noise.

Figure 2. Fingertip sensor Figure 3. Shows our pulse detection circuit.

The IR LED is forward biased through a resistor to create a current flow.

The values of resistors are chosen so that they produce the maximum amount of light output. The

photo-resistor is placed in series with the resistor to reduce the current drawn by the detection

system and to prevent short-circuiting the power supply when the photo resister detects no light.

Amplification and Filter Stage

The filter/amplifier circuit is a standard design and is documented in many sources (e.g. 0).

The signal from the IR sensor is very weak where the voltage is just around 50µV, containing a

significant noise level. The signal is affected by interference caused resulted from movement of

artefacts like rings and mains 50Hz. It is known that the standard ECG where the limits of

integration are determined from our knowledge of the signal and the time of observation. ECG

signal has frequency components in the range 0.05-200Hz. If filtered to the range 0-50Hz, the signal

does not suffer any significant loss of quality or information within the signal. The filtering process

is necessary to block the higher frequency noise components present in the signal. A capacitor of

1µF value at the input of each stage is required to block the dc component in the signal

Physical Properties

The device operates using a 9V-battery source, which should last for one year under normal

use. The package is small, lightweight and portable. The cost of the HRM device is kept to the

minimum in order to maintain a competitive edge with products currently available in the market.

The current estimate of the cost of the components is ~SDG150.

The microcontroller is the main component in our device. It acquires the ECG signal via the

ADC, computes the heart rate, and controls the LCD, keypad and GSM modem. The

microcontroller used in this study is the ATMEGA32. The driving software component includes the


50

calculation algorithm to measure the heart rate. The overall flow of the software application is

depicted in Fig. 4.

SYSTEM SOFTWARE

Discrete Fourier Transform

Determination of heartbeat bps depends on computing the Fourier Transform of the

heartbeat signal. Assuming a relatively high heart rate of 120 bpm, we can compute the minimum

sampling rate using the Nyquist-Shannon sampling.

Let us assume that a total N samples were collected during a time duration of T. If the time

between samples is ∆t, then the signal could be expressed as a piece wise step level, sample

and hold, as:

g (t) = g (ti ) where i∆t ≤ t < (i + 1)∆t---(1)

The Fourier Transform could be computed using the discrete data acquired by the ADC as follows:

G( f ) = ∑ g (t )e − j 2πfti -------------(2)

The real and imaginary components are thus given as

Re(G( f )) = ∑ g (ti ) cos(2πfti ) ----------- (3)

Im(G( f )) = −∑ g (ti ) sin(2πfti )-----------------(4)

Heart Rate Range

Our device computes the bps and compares the measurement against the maximum safe limit for the

subject in question. The maximum safe bpm value is computed depending on the gender of the

subject and his/her age. A number of methods for the maximum safe bpm are used in the medical

profession, including Martha, Londeree-Moeschberger, Miller and other techniques 0. For our

study, we adopted the formulae used by UK practitioners to compute the upper limits, HRMax as:

HRm=216 − 1.09 × Age of femael

HRm=202 − 1.09 × Age of Male

The algorithm below summarises the software:

Initialise input and output Ports

Enter user data

Forever Do

Acquire smples from ADC (5 Seconds) Compute Fourier components

Find Hearbeat rate

Display rate on LCD

If HR is outside the safe range

Send SMS msg to assigned person (if not already sent)

Switch Buzzer ON Else

Switch Buzzer OFF (if already ON)

Endif

Endforever


51


Fig. 4 shows the analogue signal acquired by the sensors and input to ADC port of the

microcontroller. The signal is consistent with the standard ECG signals used to measure the

heartbeat rate and is also used in other types of clinical diagnosis. In Fig. 5 we show the frequency

analysis of a typical heartbeat signal. The Fourier Transform of the 5sec interval shows a dominant

peak power spectral density obtained from the Fourier Transform at 72 bps. The second largest

peak, i.e. the second harmonic of the heartbeat rate, is located at 144bps. Note that the algorithm

implemented in this study searches only for the rate with the highest spectral density.

Figure 4. Analogue signal

The final device was used to measure the heartbeat rate of a number of male and female volunteers.

The results as well as the bps measured simultaneously using the heartbeat pattern of the same

volunteers as displayed on the oscilloscope are shown in Table. 1. These results show excellent

agreement

Figure 5. Fourier analysis and curve fitting


52

Table 1. Heart beat rate measurement using the developed device and via an oscilloscope

Gender

Age

HR

on LCD

HR

on scope

Error %

Male 22 97 96 1.03

Male 22 83 81 2.41 Male 20 78 78 0 Male 22 90 87 3.33 Male 20 80 79 1.25

Female 22 77 77 0 Female 22 104 103 0.96 Female 19 75 75 0 Female 20 69 71 2.81 Female 22 83 85 2.35

Table 2. Measurements of heartbeat rate before and after exercise

Age Condition HR

(bps)

HR

Normal

(bps)

24years

Before

exercise 65 64

After

exercise 90 88

15

years

Before

exercise 91 88

After

exercise 110 100

CONCLUSIONS

The design and development of a low cost HRM device has been presented. The device is

ergonomic, portable, durable, and cost effective. Tests have shown excellent agreement with actual

heartbeat rates. This device could be used in clinical and nonclinical environments. Individual users,

e.g. athletes, can also easily use it during sporting activities. The device could also be used as a

monitoring instrument exploiting the SMS capabilities provided by this system.

This study used the standard Fourier Transform to compute the spectral density. The overall

efficiency of the device could be improved by the use of Fast Fourier Transforms.

The device could be further developed into a continuously Monitoring device that could be used to

detect the heart beat anomalies associated with certain heart conditions. This would be made

possible by analyzing the heartbeat signal in the frequency domain.


53

REFRENCES

[1]Leslie Cromwell,” Biomedical instumentation and mesurment” 2nd edition Printice Hall of India

Pvt. Ltd. New Delhi 2004,p.150-160.

[2] R.S. Khandpur, “Handbook of Biomedical Instrumentation”, Tata McGraw Hill publishing

Company, New Delhi 1998, p12-125.

[3] W. J. Tompkins, “Biomedical digital signal processing”, Printice Hall of India Pvt. Ltd. New

Delhi 2004,p41

[4] M.Rayner, Coronary heart disease statistics,, British Health Promotion Research Group, Heart

Foundation Department of public health, University of Oxford, 2007.

[5] Mohamed Fezari, Mounir Bousbia-Salah, and Mouldi Bedda, “Microcontroller Based Heart Rate

Monitor”,The International Arab Journal of Information Technology, Vol. 5, No. 4, 2008.

[6]Dogan Ibrahim, Kadri Buruncuk,“Hear Rate Measurement from the Finger using a

low cost microcontro ller” http://www.emo.org.tr/ekler/a568a2a a8c19a31_ek.pdf

[5] Boashash, B., “Time-Frequency Signal Analysis and Processing: A Comprehensive Reference”,

Oxford: Elsevier Science, 2003.

[7] R. Fensli, "A Wireless ECG System for Continuous Event Recording and Communication to a

Clinical Alarm Station", Proc of the 26th Annual International Conference of the IEEE EMBS,

2004.

[8] http://www.brianmac.co.uk/maxhr.htm, Accessed on 02/09/2011

[9] Kohler, B.-U.; Hennig, C.; Orglmeister, R. The principles of software QRS detection.

Engineering in Medicine and Biology Magazine IEEE, vol. 21, , 2002 pp. 42 – 57.

[10] Piotrowskia Z.; Rózanowski K. Robust Algorithm for Heart Rate (HR) Detection and Heart

Rate Variability (HRV) Estimation. ACTA PHYSICA POLONICA, vol. 118, No. 2010, pp. 131 –

135,

http://www.brianmac.co.uk/maxhr.htm


54

Simulation Of High Efficiency Techniques For N-Type Multi-Crystalline Solar Cells

A.P. Bhat1 , S. J.Dhoble

2 , K. G. Rewatkar

3

1Department of Electronics, RTM Nagpur University, Nagpur India-33 2Department of Physics, RTM Nagpur University, Nagpur India-33

3Department of Physics Dr. Ambedkar college, Nagpur India-10

[email protected]

ABSTRACT

Research and development activities on silicon solar cells mainly focus on cost reduction

and performance optimization. An alternative technology with a large potential regarding cost

reduction and improvement of environmental reuse is n-type multi-crystalline silicon solar cell

technology. N-type multi-crystalline silicon shows several advantages compared to p-type multi-

crystalline silicon. One of them is the lower sensitivity to some metallurgical impurities, which is an

important feature when solar cells are produced from less pure silicon. In general, high minority

charge carrier lifetime and competitive diffusion length have been reported for n-type mc-Si. This

paper repors a brief overview of the n-type multi-crystalline silicon material and properties explain

in the literature, together with the behavior of n-type multi-crystalline material. Fabrication

processes for high efficiency n-type multi-crystalline solar cells based on industrial techniques are

presented.

INTRODUCTION

Today, the majority of solar cell production is based on p-type multi-crystalline silicon

wafers (mc-Si) using a very suiatble technology. However, many alternative solar cell technologies,

based on wafers or thin films, are under investigation. The overall objective is to develop a lower

cost technology and possibl use of such a materials to improved environmental footprint. N-type

mc-Si solar cells, the paper represent an alternative technology which can potentially fulfill the

objective, with current wafer utilization and cell production processes.

There is a rising interest in n-type silicon for solar cell applications: besides being an

additional silicon feedstock source for the PV production it attracted attention by a higher tolerance

to common impurities as Fe or O. The resulting higher diffusion lengths compared to p-type

combined with the reduced degradation due to the lack of B-O complexes qualifies the n-type

materia[2].

One of the advantages of n-type solar cells is that they can use of alternative silicon sources.

Due to the exponential increase of the cell production, the supply rapidly evolved into a shortage,

which may continue in the years to come. Therefore, n-type silicon is of interest because

approximately 2000 tones/year of n-type wastes of Czochralski (Cz) grown Si mono-crystals are

available[5] . Eventually after mixing with lightly doped silicon, may be used in production of n-

type mc-Si ingots by means of directional solidification. Also upgraded metallurgical silicon may

be more conveniently used for production of n-type cells, in situations where n- type dopents are

present and hard to remove. Additionally, some metallurgical impurities have lower impact in n-

type ingots. The same is true for the boron-oxygen defect.

Research and developments on solar cells based on n-type Si substrates and low-cost

screen-Printed processing became active in the recent years, and several cell structures, such as

boron- diffused emitter type, and the aluminum alloy emitter have been reported. Several



55

groups have reported very high pre and post processing minority carrier recombination lifetimes in

n-type mc-Si wafers, low recombination activity of transition impurities or very high carrier

diffusion lengths. Considering commercial-grade silicon wafers and high yeild industrial processes

inducing a wide variety of impurities and defects.

Material selection

Photovoltaic materials use inorganic semiconductors. The semiconductors of interest allow

the formation of charge-carrier separating junctions. The junction can be either a homojunction (like

in Si) or a heterojunction with other materials to collect the excess carriers when exposed to light. In

principle, a large number of semiconductor materials are eligible, but only a few of them are of

sufficient interest. Ideally, the absorber material of an efficient terrestrial solar cell should be a

semiconductor with a bandgap of 1–1.5 eV with a high solar optical absorption (104 − 105 cm−1) in

the wavelength region of 350–1000 nm, a high quantum yield for the excited carriers, a long

diffusion length low recombination velocity. If all these constraints are satisfied and thebasic

material is widely available, the material allows in principle the manufacturing of a thin-film solar

cell device.

lifetime and diffusion length

Crystalline silicon is a semiconductor material with a bandgap of 1.1 eV. Because of the

indirect bandgap character of silicon for photons with energy lower than 3.4 eV, it is clearly not an

ideal material for thin-film solar cells.

One basic reason for the selectring materrial is of high minority carrier lifetimes in n-type

silicon – compared to p-type is the lower mobility of the holes which corresponds to a lower

diffusion coefficient. That means, for the same diffusion length, the lifetime of the holes needs to

be three times higher than the lifetime of electrons in p-type Si.

Such higher lifetimes can be expected for n-type Si because of the absence of lifetime

reducing boron oxygen complexes (B-O), and lower recombination activity of transition metal

impurities. The thin film of crystalline Si can be grown either by low-temperature deposition

techniques which yield microcrystalline Si or by high-temperature techniques. the material

properties of the grown crystalline Si film are similar to the properties of bulk crystalline Si solar

material. Because of its relatively low absorption coefficient, crystalline Si layers have to be at least

30 μm thick to absorb sufficient light unless optical enhancement techniques are used to improve

the effective absorption.

III–V compound materials like GaAs, InP and their derived alloys and compounds, which

most often have a direct bandgap character, are ideal for photovoltaic applications, but are far too

expensive for large-scale commercial applications, because of the high cost of the necessary

precursors for the deposition and the deposition systems itself. The deposition systems for these

materials are either based on molecular beam epitaxy or metalorganic chemical vapour deposition.

LITRETURE REVIEW

The first functional, intentionally made PV device was by Fritts [5] in 1883. He melted Se

into a thin sheet on a metal substrate and pressed a Au-leaf film as the top contact. The modern era

of photovoltaics started in 1954 when researchers at Bell Labs in the USA accidentally discovered

that pn junction diodes generated a voltage when the room lights were on. Within a year, they had

produced a 6% efficient Si pn junction solar cell [6] By 1960, several key papers by Prince [9],


56

Loferski [10], Rappaport and Wysoski [11], Shockley (a Nobel laureate) and Queisser [12],

developed the fundamentals of pn junction solar cell operation including the theoretical relation

between band gap, incident spectrum, temperature, thermodynamics, and efficiency. Thin films of

CdTe were also producing cells with 6% efficiency [13]. In 1994, Mobil Solar Energy (MA, USA),

which had developed a process for growing solar cells on Si ribbon (called the Edge defined film

growth or EFG process) instead of more costly wafers.

Cuevas et al [1] demonstrated exceptionally high minority carrier lifetime on n-type mc-Si

material from Euro-solar SpA of varying resistivity, even approaching levels of n-type mono-

crystalline silicon.The effective minority carrier lifetime measured on mc-Si n-type material after

phosphorus (P). Deposition exceeds the millisecond lifetime mark. The best result has been reached

for a 2.3 Ωcm wafer, whose average lifetime of 1.6 ms corresponds to a hole diffusion length of 1.4

mm. Ref [1] also shows the spectacular consequence of the phosphorus deposition on the

trapping effects which are frequently associated with the presence of metallic impurities. The

results obtained on a 0.5 Ωcm resistivity wafer show a lifetime increase by a factor of 10. The

lifetime also remains practically constant over a broad range of injection levels, which is a very

desirable feature for solar cell operation. A similar behaviour is found for the post- deposition

lifetime of the 0.9 Ωcm wafer, except at high carrier densities where the lifetime is affected by

Auger and emitter region recombination.

Martinuzzi et al [2] measured, on a raw n-type material voluntarily contaminated with Fe,

Co and Au (dose of 1013 cm-2), a bulk lifetime τp of around 100μs. after deposition, they reach, at

least, 300μs.

Corresponding to diffusion length values around 200 to 300 μm. Such high lifetime values have

never been observed in p-type mc-Si raw wafers, or they have been measured only after long

deposition treatments by phosphorus diffusion or [3]. In phosphorus gettered samples, the measured

values of diffusion length are higher than 500μm. The authors refer to a LBIC contrast scan map

indicating values of diffusion length and note that conversely to p-type material, they did not find

regions in which there is no improvement of the material and where the diffusion length remains

very poor (few tens of μm).

Deposition effect

Photovoltaic cells convert sunlight directly to electricity. Their principle of operation is the

same as that for photodiode light detectors. As mentioned before these devices are fabricated from

semiconductor materials, such as silicon (Si), gallium arsenide (GaAs), and copper sulfide (Cu2S)

and other materials. In a photovoltaic cell, incident sunlight photons remove electrons in the

semiconductor from their bonds so that they are free to move around inside the semiconductor

material.

Deposition of metal impurities is an essential step in the production of efficient photovoltaic

devices from relatively impure materials, such as multi-crystalline silicon. Such metals impurities

may be present in numerous forms, including substitution or precipitates of oxides, silicates or

silicides. Some of the more important metal contaminants are most dangerous when present

interstitially, such as Fe and Cr. Deposition techniques are usually very effective at removing

interstitial impurities, and since these are often the dominant lifetime-killers, large improvements in

lifetime can result.


57

Macdonald et al. [4] investigated phosphorus deposition effect performing Neutron Activation

Analysis (NAA) on mc-Si. Thanks to this measurement technique, phosphorus deposition effect was

monitored for various contaminating elements: As, Sb, Sn, Zn (substitutional), Ag, Co, Cr, Cu, and

Fe (interstitial). It turns out that phosphorus deposition does not have any effect on substitution

elements. Their inability to be gettered arises because of their much lower diffusivity than

interstitial impurities, meaning that deposition deep into the wafer bulk in the relatively short time

used is not possible. The three dopent species (As, Sb and Sn) do not introduce deep levels in

silicon, and hence they have little impact on carrier lifetimes. The ineffectiveness of deposition

then is of little consequence for these elements. While the substitution diffusers did not respond to

deposition,they show that for Ag, Co, Cr, Cu and Fe there is a definite reduction, often quite large.

These elements all diffuse interstitially, and hence have much higher diffusivity.

Impurities sensitivity

N-type mc-Si demonstrates resilience to contamination introduced during processing or

wafer formation. This is because for many interstitial metallic impurities commonly found in silicon

solar cells, the impurity capture cross section for holes is much less than the capture cross section

for electrons.

Macdonald and Geerligs [6] modelled and measured the impact of the recombination caused by

intentional Fe contamination on the low injection lifetime of n-type and p-type wafers. The results

clearly show that the n-type wafers are much less strongly affected.

Coletti et al. [7] measured the effect of Fe contamination on the minority carrier lifetime of

p- type and n-type ingots after phosphorus deposition, boron co-diffusion and hydrogenation. The

as-grown minority carrier lifetime in the iron-doped ingots is about 1–4 and 6–30 μs for p and n

type, respectively. After deposition and hydrogenation the lifetimes in the n- and p-type Fe doped

ingots are approaching each other (lifetime is about two times higher in the n-type than in the p-type

ingot). As-grown lifetime values for the n-type reference are similar to the gettered values of the n-

type Fe ingot.

Schmidt et al. [8] theoretically determined the recombination parameters of isolated Cr and

CrB pairs in phosphorus doped n- and boron-doped p- type silicon wafers. Contrary to Fe, Cr has

larger capture cross section for holes and electrons (σn=2,3.10−13 cm2 σp= 1.10−13 cm2). In

consequence, relatively low concentration of interstitial Cr in bulk Si causes large lifetime

degradation in both p- and n-type mc-Si.

Ti has diffusivity several orders of magnitude lower than Cr or Fe. Because of its low

density, titanium, once introduced, remains at interstitial sites within the Si lattice after cooling to

room temperature. Interstitial Ti produces mid-gap donor and acceptor levels with large

capture cross sections and has a pronounced influence on the lifetime of minority carriers in p- and

n-type silicon. However, Geerligs et al. Compared effective diffusion length of p- and n- type mc-

Si ingots voluntarily contaminated with Ti (fig 1). The measurement results show that the carrier

diffusion length of the n-type wafers is not affected, whereas the carrier diffusion length of the p-

type samples is


58

Figure 1 - Comparison, of n-type and p-type mc-Si ingots

Crystal impurity

The recombination rate of minority carriers in a mc-Si wafer is also related to the

interaction between impurities and crystal defects. The extended defects themselves are increase or

decrease in recombination, and in the large grains of mc-Si, dislocations are the most harmful

defects when they are decorated by impurities. Since the capture cross sections of the metallic

impurities are smaller in n- type silicon, it is expected that the consequences of the impurity-defect

interactions are reduced, and this reduction will be enhanced after deposition because of impurity

concentration decrease (ref [2]).

Martinuzzi et al. [2] made lifetime and LBIC contrast scan map of high densities

extended defects regions. Local values of minority carrier lifetime measured are at least ten times

higher than those found in a p-type sample containing similar defect densities. In a region where the

dislocation density is about 107 cm-2 , diffusion length of 120 μm and lifetime of 60μs were

measured which confirm the low recombination strength of extended defects.

Cotter et al [9] reported the excellent tolerance of n-type wafers to induced or introduced

defects. For feedstock considerations, the defects that exhibit high hole lifetime and low

electron lifetime suggest that n-type silicon wafers would be a better choice for high-efficiency

commercial silicon solar cells.Also Woditsch et al, in patent US6576831, describe that crystal

defects in n-type silicon are less active than in p-type silicon, and as a consequence, n-type mc-Si

with low proportions of active grain borders can be obtained.

Recombination activity of impurity point defects between p- and n-type mc-Si. Ref [10]

show that the as-grown extended crystal defects degrade less after phosphorus deposition in p-type

wafer than in n- type wafer. After hydrogenation, the lifetime improvement is similar for both p-

type and n-type which means no large difference in tolerance to extended defects between both

types. In conclusion, high minority carrier lifetimes and competitive diffusion length have been

reported in multi-crystalline n-type material. In addition, n-type mc-Si demonstrated resilience to

common contaminations during process or wafer formation.

Reduction of recombination activity after deposition in n-type mc-Si has been shown to be

as good as in p-type material. Crystallographic defects commonly introduced during wafer

growth, such as grain boundaries or dislocations, may exhibit low recombination strength in n-type

mc-Si, . fabrication process would lead to high efficiency silicon solar cells based on n-type mc-Si

substrates.

The main reasons for p-type mc- Si wafers are used for solar cell production are when space

power applications dominated because irradiation studies showed significant degradation of the

minority carrier lifetime and junction characteristics for n-type wafers [11]. Other reasons for the p-

type domination on the solar cell market are related to fabrication process issues such as easier

emitter formation by phosphorus diffusion. Moreover, new processes achieve excellent boron


59

emitter formation and passivation and n-type solar cells benefit from structure design advantages

such as open rear side metallization, suitable for thin wafers and enhancing internal reflection.

EXPRIMETATION

Deposition efficiency of p-type emitter versus n-type emitter

Deposition via standard phosphorus diffusions remove easily a selection of interstitial

impurities (e.g. Fe) but the possible effect of these impurities on the recombination rate in the

diffused regions is to be considered. Macdonald et al. [12] investigated whether concentrations of Fe

for both boron- and phosphorus-diffused regions can cause a measurable increase in recombination,

as characterized by the emitter saturation current density. The author established that the deposition

efficiency of the phosphorus is much greater than for boron diffusions, despite the fact that a greater

number of boron atoms are required to achieve the same sheet resistance, due to lower carrier

mobility. The extracted current density values show that even though more than 99% of the Fe is

present in the phosphorus diffused regions and glass, there is no measurable impact on the

currenty density values. However, there is a clear two- to three-fold increase in the saturation

current for boron diffused samples.

These observations can be explained by the large difference in capture cross sections for

electrons and holes for the likely forms of Fe in these samples. In the n-type multi-crystalline

bases, which are of increasing interest, iron gettered to boron-diffused emitters may still have a

significant impact on recombination

RESULTS

Fe contamination

G. Coletti et al. [7] investigated the impact of Fe on n- and p-type wafers sliced from

directionally solidified microcrystalline ingots and on performance of solar cells fabricated from

these wafers. Short circuit current (Jsc) times open circuit voltage (Voc) product for the p- and n-

type references and for the Fe contaminated ingots. The performance is remarkably close to the

reference at positions between about 65% and 72% of the ingot height for the p-type ingots. In the

n-type ingot, the addition of Fe reduces the solar cell performance in most of the ingot. Jsc×Voc is

reduced in the bottom and the middle. In the top, the performance of the n- type reference decreases,

approaching the value of n-type Fe contaminated ingot. The authors showed that the main reason for

the degradation is a reduction in the diffusion length. From spectral response and reflectivity

measurements, the internal quantum efficiency (IQE) and the effective average minority carrier

diffusion length (Leff) were calculated. The main differences between the references and Fe

doped ingots are in the long wavelength response. No increase in recombination in the emitter

region is visible in the IQE measurements differently than reported by Macdonald et al. [10].

However, Mihailetchi et al. [13] note, for the same Fe-contaminated cells, a more distinct drop

in Voc than for non-Fe- contaminated cells, and attribute this to recombination in the emitter, in

line with the findings of Macdonald. Further experimental work is needed in order to

discriminate between the possible causes.

The authors also described a difference in the crystal structure development for both the Fe

doped ingots compared to the reference ingots. At the bottom and at the top of the Fe doped ingots

the density of the crystal defects is enhanced, both in comparison to about 70% height within the

same ingots and in comparison to the reference ingots. This is reflected in the solar cell efficiencies,


60

which are reduced in the bottom and top, but are comparable to the reference at around 70% height.

The increasing defect concentration in the top of the Fe doped ingots may be related to the

increasing iron concentration in the melt. In the bottom, the initial high concentration of Fe in the

silicon melt may have originated a transient nucleation and growth disturbance during the early

solidification phase. However, these effects may be particular for the very heavy contamination (50

ppmw) introduced in these experiments

Efficiency variation

Mihailetchi et al. [13] experimentally investigated the correlation between resistivity and

solar cell efficiency on n-type mc-Si wafers. Two multi-crystalline n-type ingots grown in the same

furnace have been selected for this investigation: a compensated ingot (called ingot 5) which is

partially p-type (boron dominates over antimony) and partially n-type (antimony dominates

over boron) doped. Solar cells have been fabricated on 156.25Cm2 wafers distributed to cover a

resistivity range of0.8 to 7.7 Ωcm from the first ingot and 0.3 to 2.2 Ωcm from the second ingot.he

measured JscxVoc product increases with resistivity for cells made from ingot 6 while it stays rather

constant for cells of ingot 5 for resistivity larger than 1.3 Ωcm. These results suggest that the

optimum base resistivity for n-type multi-crystalline Si feedstock lies between 1.5 to 4Ωcm.

However, recent results in our group for an ingot of higher resistivity (described in the next

paragraphs), indicate that this result is probably dependent on ingot growth conditions, and not

universally valid. From lifetime data resulting from fitting internal quantum efficiency data (IQE),

in ref. [13] it is observed that a resistivity higher than approximately 1.3 Ωcm is required in order

to ensure that bulk diffusion length is higher than the average wafer thickness for both ingots.

The lifetime as a function of resistivity also shows, for low resistivity, a linear dependence,

suggesting activity of some impurity which is relatively harmful in n-type base (e. g. Au, Zn,

perhaps Cr).

A similar study on n-type mc-Si wafers from the Dai-Ichi Kiden company has been also

carried out in our group. The results show an increase of efficiency with resistivity, even up

to a resistivity higher than 7 Ωcm. The JocxVoc trend is actually similar to the trend described by

Mihailetchi et al. [13] but shifted to higher resistivity. The reason for the difference in efficiency

variation as a function of the resistivity is still under investigation, and could be due to different

defects in the various ingots.

Process

The n-type mc-Si material characteristics described in the previous sections offer

perspective for fabrication of high efficiency commercial solar cells. The main challenge resides

in the designing of an adapted fabrication process. One of the major development areas of the n-

type mc-Si solar cell process remains the passivation of the front side boron emitter. Since the

conventional way to passivate phosphorus emitters for the p-type solar cell process, using a

PECVD-SiNx layer, results in a poor or no passivation for boron emitters, a new way of

passivating boron doped surfaces needs to be developed. Mihailetchi et al. [13] have developed a

new method to passivate boron emitters which brought new potential to the n-type

multicrysatlline silicon industrial solar cell process. This new method relies on the same

PECVD SiNx technology, as is widely used in industry to passivate phosphorus emitters,

and is industrially applicable with no substantial increase in cost or process time.


61

This method employs an ultrathin silicon oxide between the emitter and the SiNx. An

almost 6-fold enhancement in the lifetime and 60 mV higher implied Voc is observed for

lifetime test devices after firing. These values outperform even the results obtained using

thermal SiO2/PECVD SiNx stacked layers as a passivation method. Since the method employs a

low-temperature oxidation process, possible deterioration of, e.g., the base material, is minimized.

Our simplified cell process protocol is illustrated in figure 2 and a structure of the fabricated

n-type cells is presented in figure 3. The rear-side metallization has an open structure that

can enhance the internal reflection, as well as increase the annual energy yield by employing

bifacial modules. The cell process led to efficiencies of 16.7% on multi-crystalline and 18.5%

on monocrystalline wafers of 125mm size (independently confirmed by ISE CalLab) [14]

Wafer texturing and cleaning

Emitter & BSF diffusion

Wet chemical process and

SiNx coating (both sides)

Screen printing metal paste

Firing through

Figure 2 - Major process steps for making industrial screen printed n-type solar cells.

Figure 3 - Schematic cross-section of the n-type solar cell.

In the context of the European FOXY project, modules were made of n-type mc-Si solar

cells - made from Deutsche Solar wafers by ECN using the process described above – and were

assembled and tested by Isofotón. After 3 months of outdoor exposure, no signs of degradation have

been observed. Also, on separate (mini-)modules, damp heat and thermal cycling tests were carried

out at ECN and have shown a fill factor degradation of less than 2%. Recently, Naber et al. [14]

demonstrated that an alternative wet chemical process for creating the SiO2 passivation layer

facilitates a further enhancement of the Voc by 4 to 5 mV. The Voc has (on Cz of 1 Ωcm) an

average value of 634 mV and a peak value of 639 mV.

New passivation methods for boron emitter are under development to utilise the full

potential of n- type solar cells. New technology involving negatively charged dielectric layers

such as Al2O3 are under investigation. Benick et al. [15] have proven the excellent surface


62

passivation of Al2O3 deposited by Atomic layer deposition technique (ALD) on cell level

based on float zone Si substrates. They reported very high IQE values of ~100% in the 300–

600 nm range demonstrating the excellent front surface passivation on B-doped emitters provided

by Al2O3. Atomic layer deposited Al2O3 may therefore also offer excellent passivation for n-type

mc-Si wafers.

CONCLUSION

The results presented in this paper confirm that n-type multi-crystalline silicon offers a

significant opportunity for commercial high-efficiency silicon solar cells. From a feedstock point of

view, n-type mc-Si material exhibits an excellent tolerance to a large number of impurities and it

has been reported that the effect of interactions between impurities and extended defects can be

strongly reduced compared to p-type mc-Si material. In consequence, compared to p-type, n-type

mc-Si has high minority carrier lifetime and competitive minority carrier diffusion length suggesting

that this n-type mc-Si is better suited for high efficiency commercial silicon solar cells. Simple and

cost effective concepts for solar cell manufacturing based on n-type mc-Si wafers are in

development and already led to record efficiency of 16.7% on large area multi-crystalline wafers.

One of the key process steps to reach such high efficiencies is the boron emitter passivation

Photovoltaics constitute a new form of producing electric energy that is environmentally

clean and very modular. In stand-alone installations, it must use storage or another type of generator

to provide electricity when the sun is not shining which currently outperforms the best passivation

obtained for the conventional n-type emitter on p- type wafers (Joe=23 fA/cm2 for p-type emitters

vs. Joe200 fA/cm2 for n-type emitters).

REFERENCES

[1] Andres Cuevas, Mark J. Kerr et al. pl. Physics Letters, vol.81,n°26, 2002

[2] Martinuzzi et al. J. Appl. Phys. 32, 187-192, 2005

[3] A.A. Istratov, H. Hielsmair, E.W WeberAppl. Phys. A 69, 13 (1999)

[4] Macdonald et al. IEEE - New Orleans, 2002

[5] J. Libal, L.J Geerligs et al. Photovoltaic Specialists Conference, 2005

[6] Macdonald & GeerligsAppl. Physics Letters, vol. 85, n°18, 2004

[7] Coletti, Kvande et al.J. Appl. Phys., 104, 104913, 2008.

[8] Schmidt et al.J. Appl. Phys 102, 123701, 2007

[9] Cotter et al. IEEE, vol. 53, n°8, 2006

[10] Geerligs et al.J. Appl. Phys 102, 093702, 2007

[11] K.D. Schmidt et al. Bell Syst. Tech., 1963

[12] Macdonald et al.Appl. Physics Letters 88, 092105, 2006

[13] V.D. Mihailetchi et al. IEEE, 2008


63

Unique Interfacing System For Multiple Sensor Data Acquisition And Control System Using

Virtual Instrumentation

A. P. Bhat1, N.V. Shiwarkar

2 S. J. Dhoble

3, K. G. Rewatkar

4

1Depatrment of Electronics, RTM Nagpur university Nagpur-440033 India. 2Department of Electronics, Dr. Ambedkar College, Nagpur-440010 India.

3Department of Physics RTM Nagpur University, Nagpur- 440033 India 2Department of Physics, Dr. Ambedkar college, Nagpur-440010 India.

[email protected], [email protected]

ABSTRACT

Data acquisition and control system consists of analog to digital converter (ADC), digital to

analog converter (DAC), timer, counter, pulse generator, digital input / output (DIO) depending

upon requirement. All the system components must communicate with personal computer (PC) for

data and control signal transmission via one of the communication protocol like Serial, Parallel,

USB, GPIB. Serial communication is advantageous over other protocol due to several reasons, like

long distance transmission, less number of physical connection, ease of implementation etc. The

system is developed Serial Multiple based Data Acquisition and Control System, which can control

different modules like temperatures pressure and vibration,, the interfacing card is designed using

single serial port and A Lab VIEW based program is developed for the individual communication

of each module.

Keywords: ADC, Digital system, communication methods, multiple data sensor, lab view, Virtual

instrumentation

INTRODUCTION

In the resent year numerous developments in VLSI give new era to the development of

microcontroller based system call as smart system. This development is being coupled with

numerous applications and continued with development changes compared with traditional

philosophy of data acquisition. Traditional scheme based on simple ADC interface have been

replaced in many situation where there is the need to collect information faster than a human, data

loggers can possibly collect the information and in cases where accuracy is essential. A data logger

is a device that can be used to store and retrieve the data [1]. Data logging also implies the control

of how sensor collects analyzes and store the data. It is commonly used in scientific experiments.

Data loggers automatically make a record of the readings of the instruments located at different

places. The user determines the type of information recorded. Their advantage is that they can

operate independently of a computer. The range includes simple economical single channel multi

sensor and function loggers to more powerful programmable devices capable of handling hundreds

of input [2].

The basic data acquisition and control system consists if different types of application module

like temperatures pressure and vibration etc. The module is selected depending upon the

requirement. The modules are individually controlled with personal computer (PC) for data and

control signal transmission using one of the communication protocol. If communication is done

using different protocol for different modules in system requires knowledge of different

communication protocols, communication hardware and large number of connection with the PC. In

order to overcome the above mentioned difficulties, we developed Serial Multiplexed based Data

Acquisition and Control System (SMDACS). In house developed system consists of different




64

application modules and a controller module. The application modules are controlled by controller

module having serial connectivity. The control program for each application module is developed in

Lab-VIEW environment.

RELEVANT THEORY

The task of data acquisition and logging is unique in the predefined environment is behind less

complicated system but if we defined the task of remote data acquisition with the developing

technology then the task is become complicated. The problem is resolve using microcontroller

interfacing method with the wireless communicable environment such as RF environment. This

wireless communication helps to acquire the data from the remote place and received data is show

on display device or with some extra development interface with the personal computer (PC). The

primary goal of this work is to design an digital system using AVR Atmega-16 Microcontroller

Family with their communication feature (Rx, Tx) with the RF communication module (cc2205)

communication protocol. The prototype work is to use data logging for temperature, pressure

vibration and humidity measurements. In order to meet the above requirements, a low cost,

versatile, portable data logger is designed. The temperature, pressure and Vibration acquiring is

designed using microcontroller At mega 8 and At-Mega 16. A particular value of temperature

pressure and Vibration is acquired by At mega 8 designed unit which work as slave and it send to

main controller board designed using Atmega-16 work as master control, which connected with the

PC at the data collection centre

EXPERIMENTAL WORK

A block diagram shown in Fig. 1. Consists of different application modules which are

installed on back panel of card developed using ATMega- 16 microcontroller of the system. The

physical address for the application module is set on mother board from 000 to 111. When system is

switched ON, the application module read the physical address and saves in local register of

microcontroller. While transferring command for Read / Write, the logical address is sent first with

the interrupt status value. The microcontroller in application module compares logical address and

physical address. The module program command sequence is executed in the application module

whose logical address and physical address matches. All the commands are treated as either read or

write considering as receive or send by PC. Data and commands are sending or receive by the PC to

the application module via serial interface. The application module can be installed in one to eight

locations while controller is placed on ninth position. The application module has no physical

position limitation, i.e., any module can be installed in any position except the controller module.

Figure 1: Block diagram of developed system

Temp

Lab-

View

RS 232

Interface

Controller ATMega- 16

Humidit

y

Vibratio

n

Pressur

e

LCD

DISPLAY


65

Figure 2: shows the developed SMDACS assembly.

The assembly consists of 3U size, nine slot chassis. The chassis as controller module, application

module, back panel and in-built power supply. The right-most module is the controller module.

Each application module communicates with the controller module using back panel 9 pin D-type

for transmit, receive and power. Three pins of the 9-pin D-type connector are used for physical

address of the module. The application module is used physical address for data and control

information transmission. Each application module consists of logic gates, microcontroller

(ATMega 16) and other related electronics and communicable components.

Controller Module

Controller module is the heart of the system. It is the interface module which transmits data

and control signals between PC and application module. Front panel of the module has power

indicator and a data transmission receiver indicator. It has an internal trigger though the INT1 which

is used as bus trigger for the entire application power status check module simultaneously. A 9 pin

D-type connector is used for communication using serial bus .A 9 pin serial connector on the back

panel of this module is used to transmit and receive data or control signal.

Figure 2: Developed serial multiplexed based data acquisition and control system hardware.

The system uses two types of programs for its operation namely system program and module

program. PC System program Lab VIEW as Graphical User Interface (GUI) which is used by users

DAQ REMOTE

MODULE RF

MODULE

Controller kit RS232 MODULE


66

while the Module program is the program written in the embedded c programming structured

microcontroller of the application module. The Lab VIEW GUI program controls the operation of

system as shown in the Fig 3. While executing the Lab VIEW GUI program, the following sequence

is followed:

Configure serial port by VISA resource name.

Select Station ID (logical address) and other related parameters which are to be passed to the

different application modules.

Activate required Station ID for passing the parameters (All or specific station).

Select appropriate command (Write or Read) The program can stop forcefully by Stop command.

Application Module

The Module program is written inside the microcontroller [1] of the individual application

module. When power is switched ON, the microcontroller inside individual module will read

physical address from the back panel and write it in the local memory μC. Figure 4 shows the flow

diagram of module program. The Lab VIEW program sends the logical address to application

module through serial communication. The logical address send by the Lab VIEW program and

physical address written in microcontroller memory is compared. If the match in address is found,

next commands end by the Lab VIEW program will be executed on that particular module.

Depending upon the command send by the Lab VIEW program, data / control word will be read

/write in particular application module using the serial interrupt. All the other interrupts are disabled

whenever application module places data on the serial bus.

Figure 4: Flow diagram for module program.

START

Initialization

Convert data into string

Send data to Lab View

System initiation cycle –INT1

Configure serial port

Status check for power supply

Acquire a data from system

Is status

is ok?

STOP


67

Digital I/O Module

The DIO module consists of eight digital inputs and eight digital outputs. This module is

developed using inbuilt ADC of the microcontroller. The ATMega series microcontroller ic have

10 bit ADC, the module read the digital input and displays the status of each bit on the Lab-VIEW

GUI. The different digital pattern is generated by setting the bit pattern in the GUI. The GUI

transfers the digital pattern to the digital output port. Here we used the serial RS-232 port separately

for communication between microcontroller and Lab View GUI.

Digitizer Module

The diagram of the developed 10bit digitizer module using ADC. The module is initialized

by the number of sample to read and the mode of trigger. The ADC module continuously read the

required number of samples after getting start trigger and system status check. The start trigger of

the module is selected using software or external hardware trigger by GUI. The developed module

has maximum storage capacity of about 64 KB. After getting the trigger, the microcontroller read

the digital data from ADC and writes the required number of sample in the memory. When module

is selected for reading the data, it will transfer data from the module memory to PC via serial bus.

The data for the “number of data bytes to be read” is written by Lab VIEW program. The lab view

coding is orange in such way that the data format is separated with the specified formatted string

separator defined in microcontroller coding. It will write the data in defined file format. User can

define a file name or append to a file. The stored data can be retrieved and analyzed as per

requirement using Origin or MATLAB software.

Communication module

The communication between the lab view coding and the microcontroller is defied with the

predefined baud rate of 9600baud. The RS232 module is configured using max 232 as TTL to

Digital logic convertor. The microcontroller sends the string of fixed length defined while

programming and lab View (VISA) port is configure with the same data rate. Serial port activation

is carryout through the VISA Read operation tool available in lab View. The received string is

display in specific string constant format with the string separator.

RESULT

The data capture by the microcontroller ATMega 16 is converted into string format using the

standard library function and send through the serial port which is already defined in the code

wizard. Figure 6 shows the snap shot of the serial port data , the independent line shows the string

data printed on hyper terminal, the same data is received in the designed lab view panel. The lab

view and microcontroller is configured with the tool VISA available in library. The received string

is stored at location and same string is used with string splitter tool with the common separator

symbol. The separate logic of string to numeric converter the string data is converted into the

numeric floating point data.

The data acquired by the microcontroller is shown on the LCD display attached with the

microcontroller-developed board.


68

Figure 5: hyper terminal data output by microcontroller

CONCLUSION

The developed SMDACS is stand alone and used in small experiment. The designed

system is compact, stand-alone, reliable, accurate and portable with on-board display of the

acquired the data from remote place or system under observation. The properly designed Data

Acquisition system saves time and money by eliminating the need of service personal to visit each

site for inspection, data collection logging or make adjustments.

The system can be used for acquiring slower sampling data for longer duration using

digitizer module. Other than this the module generates different timing pulses using TTL delay

generator to synchronize with other system. The system also generate digital pattern or to acquire

system status using digital input / output module. The analog signals generated using digital to

analog converter is used for analog pattern generation.

ACKNOWLEDGMENT

The author will thank to the National Instrument (India) Ltd. for providing the real time data

analysis tool and software support.

REFERENCES

[1] Muhammad Ali Mazidi and Janice Gillispie Mazid i, “The 8051 Micro controller and embedded

system using assembly and C”, second edition printice hall of India Pvt. Ltd .2005 PPP250, 267, 84

[2]Ayala K.J “The 8051 Microcontroller Architecture programming and Application penram

publication International ( India) Second Edition 1996.ppp.54,59,68

[3]Hall D.V, “Microprocessor and interfacing programming Hardware”, Tata Mc Grow-Hill

Edition,1991, seventh Reprint 1995.P344

[4]Johnson C.D, “The process control Instrumentation Technology ’’ Prentice-Hall (India) seventh

edition, August-2002.

[5] A. J. Thompson, J. L. Bahr and N. R Thomson, Low power data logger, proceedings of

conference department of physics, university of Otego, Dunedin2012


69

A Review Paper On Magnetic Nanoparticles Ferrites Used In Biological Applications

P. K. Tembhurne, K. G. Rewatkar, S. J. Dhoble

Dr. Ambedkar College, Department of physics, Nagpur-10 India

Department of physics, University campus, Nagpur -33, India

ABSTRACT:

Nanocrystalline ferrites are the subject of interest because of its wide application in industrial and

research area. But at present it had improved a lot curiosity in the case of nano bio-applications.

Nanoparticles have many magnetic, electrical properties which used to diagnosis the disease from

our body. This paper explains in details about biomedical application such as target drug delivery,

tumour, cancer diagnosis and magnetic resonance imaging contrasting agent etc. New developed

material are characterised with magnetic behaviour used in biomedicine application characterized

by XRD, SEM, TEM, VSM, which is useful for medical applications.

Keywords: Ferrites, biological application, XRD, SEM, TEM, VSM

INTRODUCTION

Ferrites are the ferromagnetic materials which possess the combined properties of magnetic

conductor and electrical insulator. They have been extensively investigated and being a subject of

great interest because of their importance in much technological application such as antenna rod,

transformer cores, magnetic data storage etc [1]. These electrical and magnetic properties are

affected by the type of substituent, microstructure, chemical composition and method of preparation

[2,3].

In the recent year, nanosized spinel ferrites particles received a considerable attention because

of their interesting magneting properties in biomedical application [4, 5]. It is found that when

particle diameter reduce to nanometre dimension spinel ferrite particles may exhibit super

paramagnetic behaviour, which is of great interest from the point of view of their application. The

earliest known biomedical use of naturally occurring magnetic materials involves magnetite (Fe3O4)

or lodestone which was used by the Indian surgeon Sucruta around 2,600 years ago. Current areas in

medicine to which magnetic biomaterials can be applied include molecular and cell biology,

cardiology, Neurosurgery, oncology and radiology.

We begin with a discussion of the application of magnetic biomaterials. Magnetic

nanoparticles can be applied to cell separation, magnetic resonance imaging (MRI), drug and gene

delivery, radionuclide therapy, and hyperthermia [6]. Physical properties of magnetic materials

attractive for biomedical applications because they can be control by an external magnetic field.

This is useful for separation and drug targeting. And hysteresis and other losses occur in alternating

magnetic fields are useful in hyperthermia application.

1] Drug Delivery

It is known that, chemotherapy is not always effective. In chemotherapy injected drug affect the

other than that body part where it is not required.

In the case of targeted drug delivery, the magnetic particle first acts as a carrier of the drug

which is coated. Once the drug coated particles have been introduced into the bloodstream of the


70

patient, a magnetic field gradient, created, e.g., by a external Strong permanent magnet is used to

“hold” the particles at the targeted region.

2] Hyperthermia

Hyperthermia is a type of cancer treatment in which body tissue is exposed to high

temperatures, using external and internal heating devices. Hyperthermia is almost always used with

other forms of cancer therapy such as radiation and chemotherapy

In the case of magnetic hyperthermia applications, a different principle is involved; we wish to

raise the temperature to about 43oC in a localized area in order to destroy cancer cells selectively.

This can be done by applying a magnetic field which varies with time; ferro- and ferri-magnetic

material will be repeatedly cycled through the B-H loop, resulting in hysteresis and other losses

which are then converted to thermal energy and result in an increase in temperature. Super

paramagnetic materials can also be heated using this technique.

3] Magnetic Resonance Imaging (MRI)

MRI (Magnetic Resonance Imaging) scanning is a medical investigation that uses an exceptionally

strong magnet and radio frequency waves to generate image of our body.

So far, we have only considered magnetic properties associated with the electrons in the

material. However, protons also have a magnetic moment, and this can be utilized in the powerful

imaging technique of magnetic resonance imaging (MRI). An MRI scan is one of the most

sophisticated diagnostic tools available to help a referring clinician understand the cause of our

particular health issue.

The phenomenon of magnetic biomaterials can also be applied to a no. Of biomedical application

like radionuclide delivery, cell separation, isolation of biologically active compound, modification

and for detection any diseases.

CHARACTERISTIC

Iron containing transition metal oxide phases have been the subject of extensive investigation.

These magnetic nanoparticles ferrites can be obtained in three different crystal systems like cubic

crystal structure (MFe2O4), hexagonal crystal structure (MFe12O19), and Garnet (R3Fe5O12). Magnetic

materials in the form of nanoparticles, mainly magnetite (Fe3O4), are present in various living

Organisms and can be used in a number of applications. Magnetic nanoparticles can, of course, be

prepared in the laboratory by means of the well-known methods; as sol-gel [7], hydrothermal,

reverse micelle synthesis [8], co-precipitation method [9], and ball milling technique [10].

1] XRD

The crystal structure of the materials was determined with X-ray diffraction (XRD) carried out on a

Bruker- AXS D8 Advanced diffracto meter with Cu Kα radiation in the 2θ range.


71

Fig.1 shows the x-rd pattern of spinel ferrites.

The X-ray diffraction patterns of the synthesized ferrite nanocrystals have been shown in Fig. The

peaks in XRD patterns illustrate the characteristic peaks of single phase cubic spinel structure. Peak

intensity is indicative of high degree of crystallinity of prepared ferrites. The existence of the (220),

(311), (222), (400), (422), (511) and (440) major lattice planes in the XRD patterns confirms the

formation of spinel cubic structure with the Fd3m space group, which is consistent with the powder

diffraction file of JCPDS [11].

EDAX (energy dispersive analysis of x-ray) analysis is generally carried out to test the purity

of the sample by giving us the details of all the elements present in the given sample.

2] VSM (vibrating sample magnetometer)

Magnetic characterization of the samples was carried out by vibrating sample magnetometer at

room temperature with a maximum applied field.

The obtained M-H curves show coercivity (Hc), remanence (Mr) and saturation magnetization

(Ms) which indicates the property of the samples shown in fig.2]. The absence of saturation,

remanent magnetization, and coercivity in the M–H curves indicate the super paramagnetic nature

of the particles. The non-saturation of the magnetization even at the highest applied field also

implies the presence of the single domain nanoparticles in the super paramagnetic state. The

coercivity of sample dependence on mean particle dimensions in the range of 9-40nm.The expected

particle size for biomedical application should not be greater than above mentioned size.


72

3] SEM and TEM

Morphology of the prepared samples was studied using scanning electron microscope (SEM) where

the secondary electron images were taken at different magnifications to study the morphology. The

scanning electron microscopic image of synthesized sample shown in fig. SEM micrographs show

that the grains have almost homogeneous distribution with spherical shape and agglomeration

between the particles.

Fig.3 shows the SEM image of ferrite

From the TEM image we can find the exact particle size with no agglomeration and also conform

the morphological structure.


73

Fig.4 shows the TEM image of ferrite

DISCLOSURE:

Magnetic nanoparticle can be synthesized by many methods. It is used in medical application to

cure the dieses like drug delivery, MRI, hyperthermia etc. And synthesized sample characterized by

the XRD, VSM, SEM and TEM.

REFERENCE

[1] S.Muralidharan, V.Saraswathy, L.J.Berchmans, K.Thangavel, K.Y. Ann, 2010. Sensors

Actuators, B: Chemical, 145: 225-231.

[2] A.M.Samy, H.M.EI-Sayed, A.A.Sattar, J. Phys. Stat. Sol. (a) 200 (2) (2003) 401.

[3] S.Yan, Li Dong, Z.Chen, X.Wang, Z.Feng, J. Magn. Magn. Mater. 353 (2014) 47-50.

[4]. Colombo, M.; Carregal-Romero, S.; Casula, M.F.; Gutierez, L.; Morales, M.P.; Bohm, I.B.;

Heverhagen, J.T.; Prosperi, D.; Parak, W.J. Biological applications of magnetic nanoparticles.Chem.

Soc. Rev. 2012, 41, 4306–4334.

[5]. Singamaneni, S.; Bliznyuk, V.N.; Binek, C.; Tsymbal, E.Y. Magnetic nanoparticles: Recent

advances in synthesis, self-assembly and applications. J. Mater. Chem. 2011, 21, 16819–16845.

[6]. K. Raj, R. Moskowitz and R. Casciari, “Advances in Ferrofluid technology,” Journal of

Magnetism and Magnetic Materials, Vol. 149, No. 1-2, 1995, pp. 174-180.

[7] M. George, A. M. John, S. S. Nair, P. A. Joy and M. R.Anantharaman, “Finite Size Effects on

the Structural and Magnetic Properties of Sol-Gel Synthesized Powders,” Journal of Magnetism and

Magnetic Materials,

[8] Pileni, M.P., Lisiecki, I. (1993), Nanometre metallic copper particle synthesis in reverse

micelles.80, 63-68.

[9]H. Gul, W. Ahmed and A. Maqsood, “Electrical and Magnetic Characterization of

nanocrystalline Ni-Zn Fer-rite Synthesis by Co-Precipitation Route,” Journal of Magnetism and

Magnetic Materials, Vol. 320, No. 3-4, 2008, pp. 270-275. doi:10.1016/j.jmmm.2007.05.032

[10] Corrias Ennas, G., Musinu, A., Paschina, G., Zedda, D. (1997), Iron-Silica and Nickel-Silica

Nanocomposites Prepared by High Energy Ball Milling. J. Mater. Res, 2767, 12.

[11] H. P. Klug and L. E. Alexender, “X-Ray Diffraction Procedures for Polycrystalline and

Amorphous Materials, “Chapter 9, 2nd Edition, Wiley, 1974.


74

Microstructure and Magnetic Studies Of Zinc Ferrite Nano- Particles With Cobalt

Doping For High Frequency Microwave Absorber

S. T. Chattrejeeb, A. P. Bhat

a, R.M.Shingh

b, P.M. Bodele

b, S. J. Dhoble

c, K. G. Rewatkar

b

aDepartment of Electronics, RTM Nagpur university, Nagpur -33, India bDepartment of Physics, Dr. Anbedkar college,Deekshbhoomi, Nagpur -10, India

cDepartment of Physics, RTM Nagpur university, Nagpur -33, India


ABSTRACT

In zinc ferrite, the Co Zn2+ and Fe ions are distributed over the A and B sites and therefore the

formula is represented as (Zn1dFed)[ZndFe1+d]O4,where the part between the round brackets

represent the atoms at the A sites, the part between square brackets the atoms at the B sites. For bulk

zinc ferrite prepared by the conventional sol gel auto combustion method, the inversion parameter,

d = 0 which is the condition for normal spinel structure. But, d can increase up to 0.22 for as-

quenched samples [2]. In contrast to the bulk compound, the nanocrystalline ZnCoFe 2O4 system

always shows up as a mixed spinel, in which the value of d is largely dependent on the synthesis

procedure. ZnCoFe2O4 nanoparticles produced with the same particle size range exhibit variation in

the invers-ionparameter values. Zinc ferrite nano-particles are synthesized by advanced

combustion route. The nano-sized Zn ferrite characterized by X-ray diffraction (XRD), Scanning

electron micrographs (SEM) and Energy dispersive X-ray (EDX) techniques. The magnetic

properties were determined by using vibrating sample magnetometer (VSM). The preparation

method investigated brought about formation of moderate crystalline ZnFe2O4 as a single phase

with irregular shape. Both the saturation magnetization (60 emu/g) and the remnant magnetization

(20 emu/g) were found to be highly depending upon the size and crystallinity of the investigated

ferrite. Our results indicate that this method might provide a promising option for synthesizing high-

quality nano-sized ZnCoFe2O4. In this study, the microwave assisted sol-Gel combustion route

was used for preparation of zinc ferrite..

Keywords: XRD; SEM, EDX; Ms, ZnFe2O4, crystalanity,

INTRODUCTION

Ferrite material has been widely used in various technical applications including in magnetic

refrigeration, detoxification of biological fluids, magnetically controlled transport of anti-cancer

drugs, magnetic resonance imaging contrast enhancement, magnetic cell separation, magnetic

devices, switching devices, recording tapes, permanent magnets, hard disc recording media, flexible

recording media, read-write heads, active components of ferrofluids, color imaging, gas-sensitive

materials and catalytic materials [1-7]. Ferrite based nano-materials show novel properties that are

often significantly different from the bulk due to fundamental changes in structural and concomitant

electronic rearrangements (induced by the reduced dimensionality) and to significant dominance of

the surface atoms. [8–10]. Among the ferrite materials, zinc ferrite that has been many

applications in various fields of industry including magnetic materials, gas sensor and

absorbent material for hot-gas desulphurization [11-14]. Recently, it was found that Zn ferrite is a

promising semiconductor photo- catalyst for various processes due to its ability to absorb visible

light, high efficiency, low cost and excellent photochemical stability. In addition, zinc ferrite shows



75

potentially wide applications in photo induced electron transfer, photo-electrochemical cells and

photo-chemical hydrogen production [15-22]. Zinc ferrite is fabricated by numerous methods, such

as ceramic method, sol–gel, co-precipitation, ball-milling technique, hydrothermal synthesis and

thermal decomposition [23-27].

In recent years, combustion synthesis of zinc ferrite has attracted the interest of many

researchers as an energy and time-saving process [31–34, 36, 37]. In addition, this method resulted

in ceramic products have high purity, chemical homogeneity on an atomic scale, small uniform

particle sizes and controlled particle shapes. In previous our investigations, the combustion route

with different fuels have been used to synthesize undoped and Li, Mg and Al,Co doped zinc ferrites

[31-34]. These studies showed that the molar ratio of fuel and doping affect the cation distribution

between the two interstitial sites of the spinel structure with subsequent modification in different

properties of the as prepared ferrites.

The present work aims to investigate the structural, morphologically and magnetic

properties of Zn ferrite sample which prepared by using the advanced combustion method. Detailed

analyses of the structural, morphologically and magnetic properties of as prepared ferrite are

discussed. The techniques employed were XRD, SEM, EDX and VSM.

EXPERIMENTAL

Materials

Zn/Fe mixed oxide sample was prepared by mixing calculated proportions of zinc and iron

nitrates with a mixture of Urea and ammonium nitrate. The mixed precursors were concentrated in a

porcelain crucible on a hot plate at 350 o

C for 10 minutes. The crystal water was gradually

vaporized during heating and when a crucible temperature was reached, a great deal of foams

produced and spark appeared at one corner which spread through the mass, yielding a brown

voluminous and fluffy product in the container. In our experiment, the ratio of the

H4NNO3: H2NCH2COOH: Zn(NO3)2.6H2O : Fe(NO3)3.9H2O were 1: 4 : 1 : 2, respectively.

The chemicals employed in the present work were of analytical grade supplied by Prolabo

Company.

Techniques

An X-ray measurement of various mixed solids was carried out using a BRUKER D8

advance diffractometer (Germany). The patterns were run with Cu K radiation at 40 kV and 40

mA with scanning speed in 2 of 2 ° min-1

. The crystallite size of Zn-ferrite present in the

investigated solids was based on X-ray diffraction line broadening and calculated by using

Scherrer equation [38].

B

d

2cos

where d is the average crystallite size of the phase under investigation, B is the Scherrer

constant (0.89), is the wave length of X-ray beam used, is the full-with half maximum

(FWHM) of diffraction and is the Bragg's angle. Scanning electron micrographs (SEM) were


76

recorded on SEM-JEOL JAX-840A electron microanalyzer (Japan). The samples were dispersed in

ethanol and then treated ultrasonically in order disperse individual particles over a gold grids.

Energy dispersive X-ray (EDX) analysis was carried out on Hitachi S-800 electron

microscope with an attached kevex Delta system. The parameters were as follows: accelerating

voltage 10, 15 and 20 kV, accumulation time 100s, window width 8 μm. The surface molar

composition was determined by the Asa method, Zaf-correction, Gaussian approximation.

The magnetic properties of the investigated solids were measured at room temperature

using a vibrating sample magnetometer (VSM; 9600-1 LDJ, USA) in a maximum applied field

of 15 kOe. From the obtained hysteresis loops, the saturation magnetization (Ms), remanence

magnetization (Mr) and coercivity (Hc) were determined.

RESULTS

XRD investigation

The XRD pattern of the as synthesized solid is shown in Fig.1. This figure showed that the

as prepared sample consisted entirely of nano-crystalline ZnFe2O4 particles. Indeed, the XRD

pattern contains ten sharp lines coincide with the standard data of the cubic spinel Zn ferrite

(Franklinite) phase with the Fd3m space group (JCPDS card No. 74-2397). The peaks of the as

prepared solid indexed to the crystal plane of spinel Zn ferrite (220), (311), (222), (400), (422),

(511), (440), (620), (533) and (622), respectively. The crystallite size of this ferrite was estimated to

be about 52 nm from the X-ray peak broadening of the (311) peak using Scherrer’s equation. The

X-ray pattern of the as prepared ferrite displays sharp and well-resolved diffraction peaks with the

good crystallinity of the as prepared specimen. No additional peak of the second phase was

observed in the XRD pattern, showing that the as prepared ferrite consisted of single spinel

ZnCoFe2O4 phase.

Figure 1. XRD pattern for cubic spinel ZnFe2O4 nano-particles.

An X-ray data enable us to calculate the different structural parameters such as the

lattice constant (a), unit cell volume (V), X-ray density (Dx), the distance between the magnetic

ions (LA and LB), ionic radii (rA, rB) and bond lengths (A–O and B–O) on tetrahedral (A) sites

and octahedral (B) sites of cubic spinel structure for the produced zinc ferrite crystallites. The


77

calculated values of a, LA, LB , rA, rB, A–O and B–O of Mn ferrite are 0.8444, 0.3656, 0.2985,

0.0552, 0.0719, 0.1902 and 0.2069 nm, respectively. Whereas, the value of V is 0.602 nm while the

value of Dx is 5.3207 g/cm3

.

SEM measurement

SEM micrographs of as-prepared powders with different magnifications are shown in Fig.

2a-d. This figure displays the formation of spongy and fragile zinc ferrite powders. The fracture

surfaces of the aggregated powders are formed by using a mixture of glycine with ammonium

nitrate. In addition, the as synthesized sample consisted of multigrain agglomerations with small

discrete crystallites. One can see voids and pores in the samples. This observation could be

attributed to the release of large amount gases during combustion process due decomposition of

both glycine and ammonium nitrate. By comparing with my previous work, it is found that the

zinc ferrite prepared by using a mixture of urea and ammonium nitrate displays week

agglomeration.

Figure 2. SEM images for ZnFe2O4 nano-particles with different magnifications.

Energy dispersive X-ray (EDX) analysis of the as prepared specimen was carried

out at different voltages and various areas on the surface of solid. This finding shows almost

homogeneous and uniform distribution of Zn and Fe particles in the powder sample.

Magnetic properties

The saturation magnetization (MS), remanent magnetization (Mr) and the coercivity of the

as- prepared powders were determined by measuring the magnetic hysteresis loop (not given) at

room temperature. The MS value was found to be 60 emu/g and the value Mr was 20 emu/g for the

ZnFe2O4 sample. The corresponding squareness ratio (Mr/Ms) was found to be 0.333. In addition,

the coercivity of the investigated sample was found to 50 Oe. . It was found that the as-prepared

Zn ferrite particles in this work exhibited a saturation magnetization greater than that of ZnFe2O4,

prepared by glycine as fuel [32].

DISCUSSION

Spinel zinc ferrite, ZnFe2O4, based materials can be prepared via sol-Gel reaction between

ZnO and Fe2O3 [28]. The enhancement of this reaction is controlled by thermal diffusion of Zn

and Fe cations through the zinc ferrite film which covers the surfaces of grains of reacting oxides


78

(ZnO and Fe2O3) and acts as energy barrier. The precursor compounds, preparation method

and preparation onditions have different effects on solid state reaction between ferric and zinc

oxides to produce Zn ferrite. [40, 41].

Formation of zinc ferrite nano-particles with moderate crystallization and low

agglomeration can be achieved via the combustion route by using a mixture of glycine and

ammonium nitrate depending upon the released heat and gases during the combustion process. So,

the use of ammonium nitrate is promising route for formation of moderate crystalline zinc ferrite

nanoparticles due to distribution of the energy inside the whole reacting particles reducing

the aggregation process as shown in SEM micrographs. Also, XRD measurement showed that Zn

ferrite prepared by a mixture of glycine and ammonium nitrate has crystallinity less than that

prepared by glycine only [32]

The presence of any Fe3+

ions in ZnO by diffusion would contribute to the chemically

created vacancies depending upon the ionic radii of ferric and zinc speices are 0.064 and

0.074 nm, respectively [32]. Indeed, 3Zn2+

could be replaced by 2Fe3+

and a vacancy because of

electro-neutrality restrictions. However, ZnO–Fe2O3 system shows limited solid solution of

Fe2O3 in ZnO solid. Ferric cations which appear in tetrahedral sites with the introduction of

trivalent cations into ZnO can be considered as an embryonic element or nucleus for formation

of inverse spinel in order to satisfy energy stabilization in the structure [44] .On the other hand,

Fe3+

cations have a tendency to be located in tetrahedral sites with making a strong bond with

O2−

ions in terms of electro-negativity differences and reach the lowest state of energy.

In this work, the observed super-paramagnetic behavior of Zn ferrite nano-particles could

be attributed to spin canting and surface spin disorder that occurred in these nano-particles

[45, 46]. The large value of magnetization observed in the present study shows that the

cation distribution changed from normal to mixed spinel type. Hence, the percentage of Fe3+

ions occupies the tetrahedral sites which switches on the A–B super-exchange interaction and gives

rise in the magnetization. EXAFS studies conducted by Jeyadevan et al. support the presence of

Zn2+

ion on the B-sites [48]. Liganza found that 4% of the A-sites was occupied by Fe3+

ions

[49]. The neutron diffraction study of nanocrystalline ZnFe2O4 reports that the occupancy of

Fe3+

ions at the A sites is 0.018 and 0.142 for the fine particles of diameters 16, 17, 26 and 29

nm, respectively.

CONCLUSIONS

We have Prepared ZnCoFe2O4 sample by solgel method and performed structural and

morphological study and its particle size. The crystalline size of synthesis nanocrystal was

calculated by Debye sheerer Formula the particle size in the range of 26nm. The Xray diffraction

measurement the formula of indicates the formula of single phase cubic Spinel Ferrite with the

space group Fd3M and distribution. From the SEM image it is calculated that the Material is

moderately agglomerated at low magnification.

Using a mixture of Urea and nitrate as fuel resulted in formation of Zn ferrite with

moderate crystalline cubic spinel structure, homogeneously distributed nanoparticles and nano-


79

scale size. Higher saturation magnetization (60 emu/g) and coercivity values (50 Oe) of Zn ferrite

are obtained by using a mixture of glycine and ammonium nitrate as fuel. These values are greater

than those for nano-magnetic Zn ferrite materials prepared by using glycine only.

ACKNOWLEDGEMENT

Author would thank to UGC-DAE Consortium center Indore, for material synthesis and Scientific

discussion.

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1. N. M. Deraz, S. Shaban, J. Analyt. Appl. Pyrolysis, 86 (2009) 173.

2. N. M. Deraz, M. K. El- Aiashy, Suzan. A. Ali, Adsorp. Sci. Technol. 27(2009)803.

3. N.M. Deraz, S.A. Shaban, A. Alarifi, J. Saudi Chemical Society 14(2010)357.

4. Y. KÖseoglu, A. Baykal, F. Gzüak, H. Kavas, Polyhedron 28 (2009) 2887.

5. Shao-Wen Cao, , Yue-Hong Huang, J. Hazard. Mater. 171 (2009) 431.

6. Z.H. Zhou, J.M. Xue, J. Wang, H.S.O. Chan, T. Yu, Z.X. Shen, J. Appl. Phys. 91(2002) 6015.

7. Y. KÖseoglu, G.S. Alvarez, M. Toprak, M. Muhammed, Phys. Status Solidi B 242 (2005) 1712.

8. M. Tsuji, Y. Wada, T. Yamamoto, T. Sano, Y. Tamaura, J. Mater. Sci. Lett. 15 (1996)156.

9. J.W. Choung, Z. Xu, J.A. Finch, Ind. Eng. Chem. Res. 38 (1999) 4689.

10. A.J. Rondinone, A.C.S. Samia, Z.J. Zhang, J. Phys. Chem. B (2000) 7919.

.


80

Thermal, UV & Magnetic Studies of Complexes of Ethyl Xanthates with Co(III),

Fe(III), Ni(II) and Zn(II)

S.S. Sakhare

M.M. College of Science, Nagpur

ABSTRACT

The ethyl xanthates complexes of Co(III), Fe(III), Ni(II) have been prepared and

characterized by elemental analysis and infrared studies. The thermal studies of these complexes

have been carried out. It was observed from the TG curves that Co(III), and Fe(III) complexes

decompose without any break to oxide and sulphate respectively, as the final product whereas Ni(II)

complex decomposes directly to Nickel sulphide where as Zinc (II) complex first decomposes as

zinc sulphide followed by decomposition to zine oxide as the stable end product. Some spectral,

magetic & thermodynamic parameters, e.g. U.V., activation energy, frequency factor, xH, xS, xG

were computed from Sharp Wentworth method by using Arrhenius equation.

INTRODUCTION

Xanthate usually refers to a salt with the formula ROCS2M+ (R = alkyl; M+ = Na+,

K+(1,2))

As early as 1815 , Zeise prepared the first xanthates and analyzed some of their potassium, sodium,

barium, lead and copper salts (1). He first coined the empirical name “Xanthate” for these

compounds because of the characteristics yellow color of the copper complexes. Thermal studies

on metal xanthates have been reported[2], but very little work has been done on the determination

of magnetic properties & kinetic parameters of these complexes [3,4]. The present paper deals

with the magnetic properties, U.V., I.R., Thermal Studies & determination of kinetic parameters of

ethyl xanthate complexes of Co(III), Fe(III), Ni(II) and Zn(II).

EXPERIMENTAL

Cobalt, Iron, Nickel and Zine complexes were prepared[5] by adding aqueous solution of

metal chlorides to the aqueous solution of the potassium salt of the ligand and refluxing for one

hour when soild mass crystallized out. The product was filtered, washed several times with water

and then dried in air and stored in desiccator over fused CaCl2. The ligand ratio was kept 1:2 for

Ni(II) and Zn(II) while that in case of Co(III) and Fe(III) was 1:3. Xanthate salts are produced by

the reactions of an alcohol with sodium or potassium hydroxide and carbon disuphide (6) (7)

ROH + CS2 + KOH → ROCS2K + H2O

Xanthates bind to transition metal cations as bidentate ligands. The charge-neutral complexes are

soluble in organic solvents.[8]


81

Structure of typical metal tris(ethylxanthate) complex.[9] The complexes were characterized

by elemental and IR analyses. Thermogravimetic analysis was carried out in air as carrier gas using

TGS-2, Thermogravimetric Analyser with TADS computer system (Perkim-Elmer). The powder

samples were collected between 300 to 400 cieves (5 to 10 mg) and heating rate was maintained at

100C/min. UV-Visible or electronic spectra of ligands and all complexes were recorded at room

temperature in chloroform in 190 to 700 nm range by using UV-240 Shimadzu automatic

recording beam spectrophotometer.

Infrared spectra of the samples were recorded on a SPECORD-75 spectrophotometer at the

Regional Sophisticated Instrumentation Centre, (RSIC), Nagpur. Spectra were recorded by using

KBr pellets technique in the frequency range 4000-400. Magnetic susceptibility of the co-

ordination complexes were determined by Gouy’s (10, 11, 12) method at room temperature at the

Department of chemistry, Nagpur University, Nagpur.


Data on physical characteristics, elemental analyses and thermogravimeric analysis of the

complexes are listed in Table 1. Table 1. Physical characteristics, elemental and TG analyses of

ethy 1 xanthate complexes of Co(III), Ni(II) and Zn(II)

Complexes

Co(OCHCS)2 5 2 3

Fe(OCHCS)2 5 2 3

Ni(OCHCS)2 5 2 3

Zn(OCHCS)2 5 2 3

Colour

Light green

Brownish yellow

Brown

White

% S

Theoretical Experimental

44.3

43.6

41.3

40.3

45.5

45.8

42.6

41.6

End product

Co O2 3

Nis

Fe(SO2 34

)

ZnO Ir Spectra Of Transition Metal Complexes With Ligand Potassium Ethyl Xanthate :

Infra-red spectra of all xanthate complexes (I.R. spectra of Fe (III) Ethyl Xanthate Fig.

3.2.25, I.R. Spectra of Zn (II) Ethyl Xanthate Fig. 3.2.29, IR Spectra of Ni (II) Ethyl Xanthate Fig.

3.2.27) Vibrational spectral Data of ethyl xanthate complex are given in table 2.

Table 2 : Vibration Spectral Data of Ethyl Xanthate Complexes of Fe (III), Co (III), Ni (II), Zn (II)

Sr. No.

Ethyl xanthate Complexes

C-O-Cin cm

-1

C-Sin cm

1-1

-C-H (streching) in cm

-1

-OH (Freestreching) in cm

-1

1.

2.

3.

4.

Fe (III)

Co (III)

Ni (II)

Zn (II)

1266

1246

1200

1273

990

1000

980

980

2987

3477

----

----

---

3450

3400

3400

C-Sin cm

2-1

1030

1040

1020

990


82

Infra-red spectra of all xanthate complexes shows a sharp band above 1200 cm-1 which

may be assigned to C-O-C linkage (ether) (13). A sharp band in Potassium Ethyl Xanthate

complexes of transition metal e.g., Fe (III), Co (III), Ni (II) and Zn (II) appears at 1266, 1246,

1200, 1273 cm-1 respectively which may be assigned to C-O-C linkage (ether). This also shows the

shifting of the C-O-C frequency in the xanthate complexes. Two sharp peaks near 1000 cm-1

appears in almost all xanthate complexes. Two sharp bands very close to each other in Fe (III), Co

(III), Ni (II) and Zn (II) xanthate complexes appears at (1000, 1040), (1000, 1040), (980, 1020),

(980, 990) respectively may be assigned to two different C-S frequencies.Free O-H frequencies

appears in Co (III), Ni (II), Zn (II), indicating the presence of hydrated water in the above

complexes as the bond appearing around 3400 cm-1 is broad and very weak.Shifting of the C-O-C

frequency in all xanthate complexes indicates the formation of complexes. Although there is no

direct evidence of the formation of bond between metal ions and sulfer atoms, the shifting of C-S

and C=S frequencies to lower frequencies and appeaeance of two C-S frequencies very close to each

other in all xanthate compexes as reported in the literature (14,15) supprots the formation of bond

between the sulphur atoms and metal ions.Magnetic & UV Properties of Xanthate complexes

Magnetic Data of Co (III), Fe(III), Ni(II) & Zn(II) Xanthate Complexes is given Table 3.

TABLE NO. 3 : Magnetic Data of Co (III), Fe(III), Ni(II) & Zn(II) Xanthate Complex.

Sr. No.

1

2

3

4

Complex Effective Magnetic Moment B.M.

Gram Susceptibility

Molar Susceptibility

Co(III) (Xanthate)

Fe(III) (Xanthate)

Ni(II) (Xanthate)

Zn(II) (Xanthate)

Zero

7.40

Zero

Zero

Zero

3100.00

Zero

Zero

Zero

2.83

Zero

Zero

Assignments of UV-VISIBLE absorption Bands of Co(III), Fe(III), Ni(II) & Zn(II) Xanthate

Complexes is show in table 4. UV-VISIBLE spectra of Co & Fe Complex shown in fig. 3.3.8 &

UV


83

Visible spectra of Ni Complex shown fig. 3.3.9 Fig. 3.3.9 U.V. spectra of Ni Xanthate complex

TABLE NO. 4 : Assignments of UV-VISIBLE absorption Bands of Co(III), Fe(III), Ni(II) & Zn(II)

Xanthate Complex

Sr. No.

1

2

3

Complex Probable StructureAbsorption Bands in nm

Assignments

Co(III) (Xanthate)

Fe(III) (Xanthate)

Ni(II) (Xanthate)

625

475

355

555

640

Octahedral

Octahedral

1A1g

1T2g

1A1g

1T2g

1A1g

1T2g

6A1g

4 4T E1g, g

1A1g

1Bg Square Panar

Fe(III) Xanthate Complex is found be magnetic in character. Cambi & co-worker (13) first

reported anomalous magnetic properties of Fe(III) complexes. Magnetic moments at room

temperature were due to equilibrium between high spin & low spin state. UV spectra of Fe(III)

Xanthate at 555 indicates Octahedral structure of complex. Magnetic study of Co(III) Xanthate

indicates Co(xanthate) is diamagnetic in nature. UV spectra at 625nm, 475nm & 355nm indicates

Octahedral structure of complex. Magnetic Study of Ni(II) Xanthate complex indicates that it is

diamagnetic in nature. UV spectra of Ni complex at 640nm indicates square planer structure of

complex. UV & Magnetic study of Zn(II) Xanthate shows that it is diamagnetic in nature. Thermal

Studies of Xanthate Complexes The TG curves of xanthate complexes of Co(III), Fe(III) and Ni(II)

between 50 to 5500C are similar in nature (Fig. 4) and expected end products are as shown in Table.

Fig. 4 Thermograms of xanthate complexes Co(III), Fe(III), Ni(III) and Zn(II)

It was observed from thermogram (Fig. 4) that the complexes of Co(III), Fe(III), Ni(II) and

Zn(II) do not contain water of hydration. Co(III) and Fe(III) complexes decompose without any

break to oxide and sulphate respectively as the final product whereas and Ni(II) complex directly

decompose to nickel sulphide. On the other hand, Zn(II) complex first decomposes directly to zine


84

sulphide followed by further decomposition forming zine oxide as the stable end product. Kinetic

parameters were calculated from Sharp Wentworth method by using Arrhenius equation and are

given in Table 5.

Table 5. Kinetic parameters of xanthates complexes of Co(III), Fe(III), Ni(II) and Zn(II).

Complexes

Co(Xanthate)

Fe(Xanthate)

Ni(Xanthate)

Zn(Xanthate)

Activation energy

kJ/mo1

199.7

42.1

53.2

68.9

Frequency factor

A

Sec--1

2.2 x 10

2.1 x 10

1.8 x 10

3.3 x 10

15

5

8

9

Decomposition

Temp.

453

438

473

433

Activation Energy

KJ/mole

119.683

42.1300

53.237

68.94

RT

KJ/mole

3.7662

3.6415

3.9325

3.5999

xH=E-RT

KJ/mole

-115.9213

-38.4885

-49.3045

+65.3401

xS

JK /mole-1

45.42

-146.10

-90.70

-65.80

x x

x

G= H-T

S

KJ/mole-136.4965

25.5033

-6.4034

93.8315

(Fig. 4.24 - Sharp-Wentworth Plot of Co (III) Xan, Fig. 4.25 Sharp-Wentworth Plot of Ni (II)

Xanthate Complex, Fig. 4.23 Sharp-Wentworth Plot of Fe (III) Xanthate Complex, Fig. 4.27 –

Sharp-Wentworth Plot of Zn (II) Xanthate Complex)

Frequency factor vary from 2.1 X 105 to 2.2 x 1015. Entropy changes S except

Co(Xanthate) shows negative values. This shows that during these decompostions reactions the

vibration of the activated complexes increases resulting into the loss of entropy. Positive values of

xH shows endothermic nature of decomposition process and negative values of xH shows

exothermic nature of decomposition process. Wandlant et. al (14) have reported low value of

frequency factor A as slow reactions and any other probable reason can not be given (15) Industrial

Applications The organosulpur (Xanthate) compounds are important in areas the production of

cellophane. Cellulose reacts with carbon disulfide (CS2) in presence of sodium hydroxide (NaOH)

to produces sodium cellulose xanthate, which upon neutralization with sulfuric acid (H2SO4) gives

viscose rayon or cellophane paper (Sellotape or Scotch Tape). Certain xanthate salts and

bisxanthates (e.g. Dixanthogen) are used as flotation agents in mineral processing. They are

intermediates in the Chugaev elimination process and are used to control radical polymerisation

under the RAFT process, also termed MADIX (macromolecular design via interchange of

xanthates).

ENVIRONMENTAL IMPACTS

Xanthates may be toxic to aquatic life at concentrations of less than 1 mg / L (16). Water downs

stream of mining operations is often contaminated (17)


85

ACKNOWLEDGEMENT

I am thankful to RSIC (Regional Sophisticated Instrumentation Center) for recording IR, thermal

data and my Guide Prof. M.N. Ray for giving valuable guidance needed for this paper

REFERENCES

[1] W.C.Zeise, Recueil de Memories del, Acad. Roy. Desscience de compenhagen, (1815)

[2] Eric Hoggarth, J. Chem. Soc., (1952) 4811.

[3] M.A. Bernard and M.M. Borell, Bull. Soc. Chim., France (1969) 3066.

[4] G.D. Ascenzo and W.W.Wendlendt, J. Thermal Analysis, 1 (1969) 423.

[5] E.E.Ried, “Organic chemistry of bivalent sulphur”, Chemical Publishing Co., New York

(1962).

[6] Roy, Kathrin-Maria (2005), "Xanthates", Ullmann's Encyclopedia of Industrial Chemistry,

Weinheim: Wiley- VCH, doi:10.1002/14356007.a28_423

[7] This report gives a detailed procedure for the potassium ethyl xanthate: Price, Charles C.; Stacy,

Gardner W. (1948). "p-Nitrophenyl sulfide". Org. Synth. 28: 82.; Coll. Vol. 3, p. 667

[8] Haiduc, I. (2004). "1,1-Dithiolato ligands". In McClevert, J. A.; Meyer, T. J. Comprehensive

Coordination Chemistry II 1. p. 349–376.

[9] Galsbøl, F.; Schäffer, C. E. (1967). "Tris (O-Ethyl Dithiocarbonato) Complexes of Tripositive

Chromium, Indium, and Cobalt". Inorg. Synth. 10: 42. doi:10.1002/9780470132418.ch6. ISBN

9780470132418.

[10]. L.H. Little G.W. Poling and J. Leja, Can J. Chem. , 39745 (1961)

[11]. M. Franzini, Z Krist, 118, 393 (1963)

[12]. T. Ikeda and H. Hogihara, Acta. Cryst., 21, 919 (1966).

[13]. L. Cambi and A. Cagasso, Att. Accad, : Naz Lincei, Ci. Sci. Fis. Mat. Nat. Rend, 13, 809

(1931); [14]. G.D. Ascenzo and W.W.Wendlendt, J. Thermal Analysis, 1 (1969) 423.

[15]. A. Mital, A.D. Kelkar and G.V. Gholap, J. Ind. Chem. Soc., 57 (1980) 517.

[16]. Besser, J.; Brumbaugh, W.; Allert, A.; Poulton, B.; Schmitt, C.; Ingersoll, C. (2009).

"Ecological impacts of lead mining on Ozark streams: toxicity of sediment and pore water".


86

Low Surface Leakage Current Of Bife2o3 Thin Films Deposited On Ito Substrates

By Using Pulsed Laser Deposition

A. P. Bhat, S. J. Dhoble, K. G. Rewatkar

Department of Electronics, RTM Nagpur University, Nagpur-440033 India

Department of Physics, RTM Nagpur University, Nagpur-440033 India

Department of Physics ,Dr. Ambedkar College, Deekshbhoomi Nagpur-440010India ABSTRACT Polycrystalline BiFeO3 thin films were prepared on indium-tin-oxide (ITO)-coated glass sub-

strates by using pulsed laser deposition (PLD). The X-ray diffraction (XRD) pattern showed a

polycrystalline perovskite phase and a (010) preferred orientation. A higher deposition tempera-

ture was required to crystallize for the BFO thin film on an ITO substrate compared to the BFO

thin film grown on a Pt substrate, the grain size was smaller than that of the BFO thin film on

Pt substrate, and the leakage current density was less. The optical transmittance was about 80%

around 780 nm, and the direct band gap (Eg ) was 2.72 ± 0.03 eV. The P − E hysteresis loop of

the BFO thin film on an ITO substrate was obtained at RT, and the polarization difference at

zero electric field (2Pro ), corresponding to the double remanent polarization was 140 µC/cm2 .

The M − H hysteresis loop was obtained at RT, and the antiferromagnetic behaviour was little

affected by using different substrates.

INTRODUCTION

Multiferroics are multifunctional materials that Si- multaneously exhibit some ferroic orders

such as ferro- electricity, (anti)ferromagnetism and ferroelasticity [1]. Moreover, they are

expected to be used for new type of devices such as magnetoelectric random access memories

(MERAMs) by using interaction between dielectric and magnetic ordering. Although many

perovskite-type oxide materials such as BiMnO3 , TbMnO3 , and BiFeO3 (BFO) have been

studied as multiferroics, BiFeO3 has attracted more attention because of antiferromagnetic

ordering with a Neel temperature (T N ) of 643 K and ferroelectric ordering with a Curie

temperature (T C ) of 1103 K [2]. Moreover, a epitaxial BiFeO3 thin film on a SrTiO3 (001)

substrate prepared by using pulsed laser deposition (PLD) has been reported to have a high rema-

nent polarization of about 60 µC/cm2 , and a polycrystalline BiFeO3 thin film on a Pt/TiO2

/SiO2 /Si substrate prepared by PLD shows a giant remanent polarization of over 150 µC/cm2 [3,4].

Recently, BiFeO3 with a large remanent ferroelectric polarization has been reported to show

photovoltaic effect and is expected to be applied to optoelectric devices [5,6]. Photovoltaic and

optoelectric applications of ferroelectric oxide ceramics have been explored in numerous

ferroelectric materials including BaTiO3 , and Pb(Zr,Ti)O3 [7,8], but are limited by a small

photo current density and a large band gap (∼3.5 eV) [5]. However, BiFeO3 is well known

to have a larger leakage current due to oxygen vacancies and other defects and a lower band

gap than many other ferroelectric perovskite materials. Moreover, the Yang and the Choi et

al. demonstrated photovoltaic effects in epitaxial films and bulks of the BiFeO3 and obtained

low band gaps of about 2.74 eV or 2.67 eV; however, their ferroelectric hystereses were not given

due to the larger leakage current [5,6]. The optical properties of polycrystalline BiFeO3 thin


87

films having a high remanent polarization deposited by using the pulsed laser deposition (PLD)

method on transparent indium tin oxide (ITO) as n-type electrode substrate can be investigated

and we expect those films to be more adequate for optoelectric applications. In this study, we

report on structural, optical, ferroelectric, and ferromagnetic properties of polycrystalline BiFeO3

thin films prepared on ITO-coated glass substrates by using PLD.

EXPERIMENTAL

BiFeO3 thin films were prepared on indium-tin-oxide (ITO, 200-nm thickness)-coated glass

substrates by using a PLD method. The fabrication of a ceramic target was started by mixing

appropriate amounts of oxide powers of Bi2 O3 (15%-excess considering highly volatile Bi) and

Fe2 O3 . The mixed powder was then calcined at 640 ◦C, followed by grinding. A disk pellet was

made by pressing the powder and sintering at 800 ◦C. The films were deposited at a

temperature around 520 ◦C and an oxygen pressure of 0.1 Torr with an ArF excimer laser (λ =

193 nm) with an energy of 130 mJ and a frequency of 5 Hz. A film thickness of 400 nm was

obtained after a 30-min deposition.

The crystalline structure of the deposited thin films was identified by using a X-ray diffraction

(XRD) analysis (Rigaku RINT 2000). The cross-sectional micrograph and surface morphology

were observed by using a scanning electron microscopy (SEM), (Hitachi, S-4800) and atomic

force microscopy (AFM), (Keyence, VN-8000). To investigate the optical properties, we

measured the transmittance by using an UV-VIS spectrometer (Varian, Cary 500). In order to

measure the electric properties and the ferroelectric P − E hysteresis loop, we formed

circular Pt electrodes of 200 µm in diameter on the thin films by RF sputtering through a

shadow mask. The leakage current density versus electric field (J −E) characteristic and the

ferroelectric hysteresis loop (P − E) were measured using a semiconductor parameter analyzer

(Agilent, 4155C) and a ferroelectric test system (ToyoCorp, FCE-1). The magnetic hysteresis

loop was measured using a superconducting quantum interference device (SQUID)

magnetometer (Quantum Design, MPMS-5S). A magnetic field of −10 kOe to 10 kOe was applied

perpendicularly to the films plane.


The crystallinity of the BiFeO3 thin films grown on ITO substrates at 470 ∼ 540 ◦C were

characterized, and the good crystallinity was obtained in the film deposited at 520 ◦C, but the

optimum temperature for the BFO thin film deposited on a Pt/TiO2 /SiO2 /Si substrate is 500 ◦C.

Figures 1(a) and (b) show the XRD (θ- 2θ) diffraction patterns of BiFeO3 thin films deposited at

520 ◦C on an ITO substrate and at 500 ◦C on a Pt/TiO2 /SiO2 /Si substrate, respectively. The

XRD patterns of the thin films were indexed for a rhombohedral structure, and the BFO thin

film grown on a Pt substrate exhibited a single-phase perovskite structure without secondary

phases. However, the BFO thin film grown on the ITO substrate had secondary phases.

Addition- ally, if the crystallization and the electric properties of the BFO thin film on the ITO

substrate are to be improved, a little higher temperature of 520 ◦C, in com


88

Fig. 1. XRD (θ-2θ) diffraction patterns of BiFeO3 thin films on (a) ITO substrates and (b)

Pt/TiO2 /SiO2 /Si substrates. S indicates peaks attributed to the substrate.

Fig. 2. (Color online) (a) Microscopic SEM cross-sectional image of a BFO thin film on an

ITO substrate and AFM images of BFO thin films on (b) ITO and (c) Pt substrates.

parison with 500 ◦C on Pt substrate was needed. The BFO thin film grown on an ITO substrate

shows a higher 010)/(110) peak intensity ratio than the BFO thin film grown on the Pt substrate.

The reason for the (010) preferred orientation of BFO thin film on the ITO substrate is not clear,

unlike the report on the BFO thin film deposited on an ITO substrate by using a sol-gel method

[9]. Figure 2(a) shows the cross-sectional SEM image of the

Fig. 3. (Color online) Leakage current density versus electric field (J − E) characteristics of

BFO thin films on Pt and ITO substrates measured at room temperature (RT).


89

Fig. 4. (Color online) (a) Optical transmittance and (b) plot of (αE )2 versus E for BFO thin

films on ITO substrates.

BFO thin film grown on an ITO substrate, and Figs. 2(b) and 2(c) show AFM images of BFO

films on ITO and Pt substrates, respectively. The thickness of the BFO thin film grown on an

ITO substrate was about 400 nm. The grain size is smaller than that of the BFO thin film grown on

a Pt substrate, thus the (020) peak width of the BFO thin film grown on an ITO substrate

becomes broader than that of the BFO thin film grown on a Pt substrate. This result is in

agreement with the results for BFO thin films grown on Pt and ITO substrates by using the sol-

gel method [10,11].

Fig. 5. P − E hysteresis loops for BFO thin films on (a) Pt and (b) ITO substrates, measured

using a 20 kHz triangular waveform at RT.

Figure 3 shows the leakage current density versus electric field (J − E) characteristics of BFO thin

films grown on Pt and ITO substrates at room temperature (RT). The J − E characteristic of the

BFO thin film on a Pt substrate is symmetric in the electric field, but that of the BFO thin film

on an ITO substrate is asymmetric as the top and the bottom electrodes are different. The

leakage current density for the BFO thin film grown on an ITO substrate is decreased compared

to that of the BFO thin film grown on a Pt substrate and the values for the Pt and the ITO

substrates at a maximum electric field of 125 kV/cm are 8 × 10−2 and 7 × 10−5 A/cm2 ,

respectively. This suggests that the film’s quality is improved and that interface property

between the BFO thin film and the ITO substrate are better than between BFO thin film and Pt

substrate, similar to result observed for a PZT thin film on an ITO substrate [12].


90

Figure 4(a) shows the optical transmittance of the BFO thin film grown on an ITO substrate,

measured in the visible region by using an UV-VIS spectrometer. The transmittance of the BFO

thin film grown on an ITO substrate was about 80% around 780 nm. To determine the band

gap, we plotted (αE )2 versus E for the BFO thin film, as shown in Fig. 4(b), where α and E are

the absorption coefficient and the photon energy, respectively. The direct band gap is 2.72 ± 0.03

eV from a linear extrapolation of (αE )2 versus E plot. This value is in good agreement with those

reported by other researchers and is lower than that other ferroelectric materials such

Fig. 6. Magnetic hysteresis loops (M − H ) of BFO thin films on (a) Pt and (b) ITO substrates,

measured at 300 K. as BaTiO3 , and Pb(Zr,Ti)O3 [5,7,8,13].

Figures 5(a) and (b) show the P − E hysteresis loops for BFO thin films grown on Pt and ITO

substrates, measured using a 20 kHz triangular waveform at RT. When the frequency of the

triangular waveform is smaller than 20 kHz, the P − E hysteresis is deformed due to the leakage

current. The BFO thin film grown on a Pt substrate shows a good P − E hysteresis loop although

the leakage current is degraded a little, and the polarization difference at zero electric field

(2Pro ), corresponding to the double remanent polarization is 206 µC/cm2 at a maximum

electric field of 555 kV/cm. The P − E hysteresis loop is also obtained for a BFO thin film grown

on an ITO substrate, and 2Pro is 140 µC/cm2 at a maximum electric field of 1230 kV/cm. The

ferroelectric property of the BFO thin film grown on an ITO substrate in this study is much

better than that (Pr ∼ 2.0 µC/cm2 ) of the BFO thin film grown on an ITO substrate by using the

sol-gel method [9]. However, the ferroelectric property for the BFO thin film grown on an ITO

substrate is worse compared to that of the BFO thin film grown on a Pt substrate. The

degradation of the ferroelectric property is thought to be affected by the preferred orientation

and secondary phases while the BFO thin film grown on a Pt substrate shows random

orientation and no secondary phases. Figures 6(a) and (b) show the magnetic hysteresis loops

(M − H ) of BFO thin films grown on Pt and ITO substrates at 300 K, for a maximum magnetic

field of 10 kOe applied perpendicularly to the film’s plane. The BFO thin film grown on a Pt

substrate shows an antiferromagnetic behavior, similar to a previous study [14].

The BFO thin film grown on an ITO substrate shows an almost linear behavior, similar to result

observed for a BFO thin film grown on an ITO substrate by using sol- gel method [10], but the

magnetization is a little smaller than that of the film grown on Pt substrate. This indicates that


91

ferroelectric property of the BFO thin film grown on an ITO substrate is changed, but the

magnetic property is little affected by the substrate.

CONCLUSIONS

We prepared polycrystalline BiFeO3 thin films on ITO- coated glass substrates by using pulsed

laser deposition. The XRD pattern showed that the BFO thin film on a ITO substrate had a

polycrystalline perovskite phase with secondary phases, and a higher deposition temperature of

520 ◦C was required to crystallize the BFO thin film grown on ITO substrate, compared to the

500 ◦C for a BFO thin film grown on a Pt substrate. Moreover, the BFO thin film grown on an ITO

substrate showed a higher intensity ratio of (010)/(110), unlike the random orientation of the BFO

thin film on a Pt substrate. From SEM and AFM measurement, thickness of the BFO thin film

grown on an ITO substrate was about 400 nm, and grain size was smaller than that on a Pt

substrate. The leakage current density was lower, the optical transmittance was about 80% around

780 nm for BFO thin film on an ITO substrate, and the direct band gap was 2.72 ± 0.03 eV. The

P − E hysteresis loop of the BFO thin film on ITO substrate was obtained at RT, and the

polarization difference at zero electric field, 2Pro was 140 µC/cm2 The M − H hysteresis curve

showed a linear behavior at RT, and magnetic behavior depended little on the substrate.

ACKNOWLEDGMENTS

The one of the author would thank s to the IITB for development of material and deposition of

material and other characterization facility.

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[3] J. Wang et al., Science 299, 171 (2003).

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[5] S. Y. Yang et al., Appl. Phys. Lett. 95, 062909 (2009).

[6] T. Choi, S. Lee, Y. J. Choi, V. Kiryukhin and S. W. Cheong, Science 324, 63 (2009).

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Photoluminescence Properties of White Light Emitting Kbapo4:Dy3+ Phosphor

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