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  • 38

    CHAPTER 2

    GROWTH AND CHARACTERIZATION OF

    1H-IMIDAZOLINIUM HYDROGEN L-TARTRATE

    SINGLE CRYSTALS

    2.1 INTRODUCTION

    Nonlinear Optical (NLO) materials are of current research interest

    in materials science for their applications in second and third harmonic

    generation, optical bistability, laser remote sensing, optical disk data storage,

    laser driven fusion, medical and spectroscopic laser (Santhanu Bhattacharya

    et al 1994). Organic molecules possess large second order molecular

    polarizability (β) and more favorable physical properties like large optical

    damage threshold and large birefringence. L-tartaric acid is a chiral

    dihydroxycarboxylic acid and it is capable of initiating multidirectional

    hydrogen bonding (Aakeröy et al 1994). The salts of tartaric acid belong to an

    important class of materials because of their interesting physical properties

    such as ferroelectricity, piezoelectricity and nonlinear optical properties

    (Second Harmonic Generation).

    The L-tartaric acid analogs were incorporated into organic salts and

    their NLO properties were widely studied in recent experiments (Renuka

    Kadirvelraj et al 1998). The nonlinear optical (NLO) properties of some

    complexes of L-tartaric acid nicotinamide have attracted significant attention

    because organic components contribute specifically to the process of second

  • 39

    harmonic generation (Haja Hameed et al 2004). The 1H-Imidazolinium

    Hydrogen L-tartrate single crystals are grown by slow evaporation solution

    growth technique. Single crystal XRD and the theoretical factor group

    analysis were carried out. The factor group analysis reveals the vibrational

    modes. The IR spectrum has been recorded to confirm the functional groups

    present in the material and the Second Harmonic Generation behaviour of

    grown crystal was studied.

    2.2 Growth of 1H-Imidazolinium Hydrogen L-tartrate single

    crystals

    The 1H-Imidazolinium Hydrogen L-tartrate was synthesized and

    grown using two different solvents. Firstly the Imidazole and L(+)-tartaric

    acid (equimolar ratio) were dissolved separately in ethanol and deionized

    water, respectively and they were mixed together. The mixture of solutions

    was found to be turbid and ethanol was added and stirred well for an hour by

    using a motorized magnetic stirrer till a clear solution was obtained. The

    solution was filtered using Whatman (grade no.1) filter paper in clean vessels

    and the vessels containing the solution were closed with perforated polythene

    cover and housed in the constant temperature bath (CTB) for growth at 32°C.

    Single crystals were obtained within 12 days and one of the harvested crystals

    is shown in Figure 2.1.

  • 40

    Figure 2.1 As grown 1H-Imidazolinium Hydrogen L-tartrate single

    crystal using ethanol as solvent

    Secondly, the equimolar (1:1) ratio of Imidazole (C3N2H4)

    (SRL-extra pure) and L (+) tartaric acid (C4H6O6) (Merck-extra pure) were

    dissolved separately in deionised water. Then the solutions of the individually

    prepared raw materials were mixed together and continuously stirred for six

    hours. The solution was filtered using Whatman (grade No.1) filter paper in

    clean vessels and the vessels containing the solution were closed with

    perforated polythene covers and housed in the constant temperature (CTB)

    bath at 32°C. The nucleation was observed in seven days and allowed to grow

    for four weeks. The reaction is shown in the Figure 2.2. The crystal of size

    15mm × 10mm × 5mm is obtained after four weeks (Figure 2.3).

    N

    NH

    H

    H

    H

    COOH

    COOH

    OH

    OH

    +N

    NH

    H

    H

    H

    COOH

    COOH

    OH

    OH

    C3N2H4 + C4H6O6 C7N2H10O6

    Imidazole L(+)-tartaric acid Imidazolinium Hydrogen L-tartrate

    Figure 2.2 Reaction Scheme of 1H-Imidazolinium Hydrogen L-tartrate

  • 41

    Figure 2.3 As grown 1H-imidazolinium Hydrogen L-tartrate single

    crystal using water as solvent

    2.3 CHARACTERIZATION OF 1H-IMIDAZOLINIUM

    HYDROGEN L-TARTRATE SINGLE CRYSTALS

    2.3.1 Single crystal XRD analysis

    From the X-ray diffraction results, it has been found that IH-

    imidazolinium Hydrogen L-tartrate belongs to the monoclinic crystal system

    with space group P21 having two molecules in the unit cell. The single crystal

    X-ray diffractometer (model Nonius CAD-4/MACH) with MoKα (0.71073Å)

    radiation was used to obtain the accurate cell parameters of the grown

    1H-Imidazolinium Hydrogen L-tartarate crystals at room temperature by the

    least square refinement of the setting angles of 25 reflections. The obtained

    lattice parameters are presented in Table 2.1, which are in good agreement

    with the reported values (Aakeröy and Hitchcock 1993).

  • 42

    Table 2.1 Crystallographic data of 1H-Imidazolinium Hydrogen

    L-tartarate

    Lattice

    parametersPresent work

    Reported

    (Aakeröy and Hitchcock 1993)

    a 7.555(4)Å 7.569(1) Å

    b 8.989(4) Å 8.993(1) Å

    c 6.961(4) Å 6.953(1) Å

    α 90° 90°

    β 101.43°(4) 101.55°(1)

    γ 90° 90°

    V 463.4(4) Å3 463.7 Å3

    2.3.2 High Resolution X-ray Diffraction Studies on ImiLT Crystal

    Good quality single crystals are much needed for device

    fabrication. The defects are discrete entities and their location and degree of

    disturbance produced in a lattice can be determined experimentally. The high

    resolution X-ray diffraction technique (multicrystal X-ray diffractometer) is a

    non-destructive analysis and can be used for direct observation of boundaries

    and dislocations.

    The high resolution X-ray diffraction analysis was carried out to

    study the structural perfection of 1H-Imidazolinium Hydrogen L-tartrate. A

    multicrystal crystal X-ray diffractometer (MCD) designed and developed at

    National Physical Laboratory has been used to study the crystalline perfection

    of the single crystal(s). Figure 2.4 shows the schematic diagram of the

    multicrystal X-ray diffractometer. In this system a fine focus X-ray source

    (Philips X-ray Generator; 0.4 mm × 8 mm; 2kWMo) energized by a well

  • 43

    collimated and monochromated MoKα1 beam obtained from the three

    monochromator Si crystals set in dispersive (+, -, -) configuration has been

    used as the exploring X-ray beam. The specimen crystal is aligned in the

    (+, -, -, +) configuration. Due to dispersive configuration, though the lattice

    constants of the monochromator crystal(s) and the specimen are different, the

    unwanted dispersion broadening in the diffraction curve of the specimen

    crystal is insignificant.

    Figure 2.4 Schematic of the Multicrystal X-ray diffractometer set up

    Before recording the diffraction curve, the specimen surface was

    prepared by lapping and polishing and then chemically etched by a non

    preferential chemical etching using the etchant of the mixture of water and

    acetone in 1:2 ratio. Figure 2.5 shows the high resolution X-ray diffraction

    curve (rocking curve) recorded with high resolution X-ray diffractometer

    using (100) diffracting planes for 1H-Imidazolinium Hydrogen L-tartrate

    single crystal. Figure 2.5 shows the DC is quite sharp without any satellite

  • 44

    -100 -50 0 50 1000

    100

    200

    300

    400

    500

    600

    Dif

    frac

    ted

    X-r

    ay

    inte

    nsit

    y[c

    /s]

    Glancing angle [arc s]

    22"

    peaks. The full width at half maximum (FWHM) of the diffraction curves is

    22 arc sec, which is close to that expected from the plane wave theory of

    dynamical X-ray diffraction. The single sharp diffraction curve with low

    FWHM indicates that the crystalline perfection is quite good. The 1H-

    Imidzolinium Hydrogen L-tartrate is a nearly perfect single crystal without

    having any internal structural boundaries.

    Figure 2.5 Rocking curve of ImiLT

    2.3.3 Spectral Analysis

    2.3.3.1 Factor group analysis

    The factor group and the site group are important in the application

    of group theoretical methods for the analysis of spectra of solids. Symmetry

    analysis is made by applying all the symmetry operations of the factor group

    to each atom in the unit cell, and reducing the representation thereby obtained

    in order to determine the number of normal modes belonging to each

    irreducible representation. An additional advantage of the factor group

    method is that it provides a basis for the prediction of the IR and Raman

    spectra of lattice vibration (Rousseau et al 1981).

  • 45

    2.3.3.1.1 Vibrational analysis of 1H-imidazolinium hydrogen L-tartrate

    1H-Imidazolinium Hydrogen L-tartrate crystallizes in the

    monoclinic crystal system with the non-centrosymmetric space group P21 and

    factor group symmetry22C . The factor group analysis of the unit cell of

    1H-Imidazolinium Hydrogen L-tartrate is carried out using the character table

    for the site symmetry group C1(2). The two molecules of the primitive unit

    cell of 1H-Imidazolinium Hydrogen L-tartrate occupy general sites of C1 (2)

    symmetry. A single molecule of 1H-Imidazolinium Hydrogen L-tartrate

    crystal contains 25 atoms which in turn gives rise to 150 modes. Group

    theoretical analysis of 1H-Imidazolinium Hydrogen L-tartrate gives 150

    vibrational optical modes which decompose into Γ150 = 74A + 73B apart from

    three acoustic modes (A + 2B). In monoclinic crystals like 1H-Imidazolinium

    Hydrogen L-tartrate, the modes have associated polarizability tensors of the

    form

    0

    0 0

    0 0

    xx xy

    yy

    zz

    A

    α α

    α

    α

    � �� �

    = � �� �� �

    0 0

    0 0

    0 0 0

    xz

    yzB

    α

    α

    � �� �

    = � �� �� �

    Here the polarizability tensors are depicted along the crystallographic

    X-, Y- and Z-axes. Both phonon A and B are Raman and IR active. The

    summary of the factor group analysis of 1H-Imidazolinium Hydrogen

    L-tartrate is presented in Table 2.2.

  • 46

    Table 2.2 Factor group analysis - Summary

    Site symmetry

    C1(2)

    Factor

    group

    symmetry

    22C Ext Int

    C H N O Optical Acoustic Total

    A 1T 3R 69 21 30 6 18 75 1 74

    B 2T 3R 69 21 30 6 18 75 2 73

    Total 3T 6R 138 42 60 12 36 150 3 147

    Analysis of the vibrational spectra reveals the information

    regarding the nature of bonding, structure of co-ordination compounds and

    material confirmation. The molecular structure of 1H-Imidazolinium

    Hydrogen L-tartrate enumerates that the title compound consist of C-H, N-H,

    and O-H groups etc. The observed vibrations of 1H-Imidazolinium Hydrogen

    L (+) tartrate could be due to lattice vibrations and internal vibration. The

    bands observed between 4000 cm-1 and 400 cm-1 in Figure 2.6 arise from the

    internal modes of 1H-Imidazolinium Hydrogen L-tartrate. The bands obtained

    below 400 cm-1 arise from the deformational vibrations and the vibrational

    and translational modes of anions and cations. Table 2.3 presents the

    correlation scheme obtained by following the procedures of Fately et al

    (1972). Each internal mode of 1H-Imidazolinium Hydrogen L-tartrate ions

    split into two components of (A(Z), B(X) and B(Y)) are IR active and

    A(αxx, αyy, αzz, αxy) and B(αxz, αyz) are Raman active.

  • 47

    Table 2.3 Correlation Scheme of 1H-Imidazolinium Hydrogen L-tartrate

    ActivitySite symmetry Factor group

    symmetry Raman IR

    74A αxx, αyy, αzz, αxy Z

    A150

    73B αxz, αyz X,Y

    .

    2.3.3.1.2 Internal Vibrations

    As the 1H-Imidazolinium Hydrogen L-tartarate molecules do not

    have any symmetry, the internal vibrations exhibited are of both IR and

    Raman active exclusive of acoustic mode. The internal vibrations of

    1H-Imidazolinium Hydrogen L-tartrate may be arising from the C-H, N-H

    and O-H functional groups. These vibrations are strongly coupled between

    themselves.

    2.3.3.1.3 External vibrations

    The bands observed below 400 cm-1 are mainly due to external

    modes. The rotational modes are expected to have higher frequency and

    intensity than translational modes in the Raman spectra. However, the

    translational modes are more intense in IR spectra (Bhatacharjee 1990,

    Hanuja and Fomitsev 1980) of 1H-Imidazolinium Hydrogen L-tartrate. It is

  • 48

    found to have (A+2B) translational and (A+2B) rotational vibrations in the

    title compound which can be achieved experimentally by polarized Raman

    measurements.

    2.3.4 Infrared Spectral Analysis

    The mid Fourier Transform Infrared spectrum of 1H-Imidazolinium

    Hydrogen L-tartrate was recorded at room temperature in the region

    4000–400 cm-1 by JESCO 416 PLUS FT-IR spectrophotometer equipped

    with LiTaO3 detector, KBr beam splitter and He-Ne Laser source boxcar

    apodization used for 250 averaged interferogram collections for both the

    sample and background using KBr pellet technique. The recorded FT-IR

    spectrum of the title compound is shown in Figure 2.6 and the functional

    group assignments were made using the standards (Martin Britto Dhas et al

    2007a, Vijayan et al. 2004). The strong broad peak at 3491cm-1 is due to the

    presence of O-H stretching in the carboxyl group. The N-H stretches of

    Imidazole ring produce broad intense signals between 2000 and 3000 cm-1.

    In the present case a very strong peak occurs at 3319 cm-1 which indicates the

    functional groups of the title compound. The peak observed at 1726 cm-1

    indicates the presence of C=O bond. The aromatic ring vibrations produce

    their characteristic peaks at 1584 cm-1 and 1410 cm-1. The sharp peak at

    1211 cm-1 is due to C-H bending vibrations of the aromatic ring. The weak

    intensity peak at 842 cm-1 is assigned to the symmetric stretch, further it is

    attributed to five membered Imidazole ring. The strong peak at 1262 cm-1 is

    assigned to the breathing mode of imidazole ring in plane C-H deformation

    (Juan Antonio Asensio et al 2002).

  • 49

    Figure 2.6 FT-IR Spectrum of 1H - Imidazolinium Hydrogen L-tartrate

    2.4 DIELECTRIC STUDIES

    Dielectric properties are correlated with the electro-optic property

    of the crystals (Boomadevi and Dhanasekaran 2004). The dielectric

    measurements of the 1H-Imidazolinium Hydrogen L-tartrate were made using

    HIOKI 3532 HiTESTER LCR meter. Good quality single crystals of 1H-

    Imidazolinium Hydrogen L-tartrate were polished on soft tissue papers with

    fine grade alumina powder. The sample was electroded on either side with

    silver paste to make it behaves like a parallel plate capacitor. The studies were

    carried out and the capacitance, dielectric loss (tanδ) and ac conductivity of

    the sample were measured as a function of frequency (50 Hz to 5 MHz) and

    temperature (in the range 35°C, 50°C and 100°C). A small cylindrical furnace

    with dimensions 20 cm × 20 cm × 20 cm was used for the experiment and the

  • 50

    temperature was controlled by Eurotherm temperature controller (±0.01°C).

    The dielectric constant was calculated using the relation

    0r

    Cd

    ε= (2.1)

    where ε0 is the permittivity of dielectric region, C is the capacitance, d is the

    thickness of the grown 1H-Imidazolinium Hydrogen L-tartrate crystal and A

    is the area of cross section of the crystal used for experiment.

    The frequency dependent dielectric constant is shown in Figure 2.7.

    The dielectric constant decreases with increasing frequency and becomes

    almost saturated beyond 10 kHz for all temperatures (35°C, 50°C and

    100°C). The higher value of dielectric constant is due to higher space charge

    polarization at lower frequency region. This may be explained on the basis of

    the mechanism of polarization similar to the conduction process. The

    electronic exchange of the number of ions in the crystal lattice gives local

    displacement of the applied field, which gives the polarization. As the

    frequency increases, at which the space charge cannot sustain and comply the

    external field. Therefore the polarization decreases and exhibiting the

    reduction in the value of dielectric constant with increasing frequency. The

    magnitude of the dielectric constant depends on the degree of polarization

    charge displacement in the crystals. The dielectric constant of materials is due

    to the contribution of electronic, ionic, dipolar and space charge polarization

    which depends on the frequencies (Dharmaprakash et al 1989). At low

    frequencies, all these polarizations are active. The space charge polarization is

    generally active at lower frequencies and high temperatures.

  • 51

    Figure 2.7 Variation of Dielectric constant of ImiLT with frequency

    The change of dielectric loss (tanδ) with frequency is represented

    for the as grown crystal in Figure 2.8. It is observed that the dielectric loss

    decreases with increasing frequency. The low value of dielectric loss indicates

    good quality (Benet Charles and Gnanam 1994) of the crystal. The larger

    value of dielectric loss (tanδ) at lower frequencies may be attributed to space

    charge polarization owing to charged lattice defects (Smyth 1965). The low

    values of dielectric loss indicate that the grown crystal contains minimum

    defects.

  • 52

    Figure 2.8 Variation of dielectric loss of ImiLT with frequency

    The conductivity of 1H-Imidazolinium Hydrogen L-tartrate

    increases with increase in temperature. The electrical conduction in dielectrics

    is mainly a defect controlled process in the low temperature region. It is

    inferred from Figure 2.9 that the electrical conductivity of 1H-Imidazolinium

    Hydrogen L-tartrate is low at low temperature owing to trapping of some

    carriers at defect sites. At any particular temperature, however the Gibb’s free

    energy of a crystal is minimal when a certain fraction of ions leaves the

    normal lattice. As the temperature increases, more and more defects are

    created, and as a result, the conductivity, which is predominantly due to the

    movement of defects produced by thermal activation, increases (Jain et al.

    1964).

  • 53

    1 2 3 4 5 6 7

    0.00000

    0.00002

    0.00004

    0.00006

    0.00008

    0.00010co

    nd

    uc

    tiv

    ity

    (S/c

    m)

    log f

    (35oC)

    (50oC)

    (100oC)

    Figure 2.9 Variation of conductivity of ImiLT with frequency

    2.5 OPTICAL STUDIES OF ImiLT Crystal

    To determine the absorption range and hence to know the

    suitability of 1H-Imidazolinium Hydrogen L-tartrate single crystals for optical

    applications, UV-Vis spectrum was recorded with 2 mm thick crystal

    between 200 – 800 nm using UV-VIS-NIR (PERKIN ELMER LAMBDA

    35) Spectrometer which covers ultra violet (200-400 nm) and visible

    (400-800 nm) region. The spectrum obtained is attributed to the promotion of

    electrons in σ, π and n- orbital from the ground state to higher state. The

    recorded UV-Vis spectrum of the title compound is shown in Figure 2.10.

    The spectrum indicates the absorbance due to electronic transition between

    338 nm and 800 nm. The cut off wavelength 338 nm may be assigned to the

    electronic transitions in the aromatic ring of 1H-Imidazolinium Hydrogen

    L-tartrate single crystals. Absence of absorbance in the region between

  • 54

    400 and 800 nm is an advantage as it is a key requirement for materials

    having NLO properties.

    Figure 2.10 UV-Vis Spectrum of 1H-Imidazolinium Hydrogen

    L-tartrate

    2.6 TGA-DTA Analysis of ImiLT

    Thermogravimetric and differential thermal analyses give

    information regarding phase transition, water of crystallization and different

    stages of decomposition of the crystal (Meng et al 1998). The

    thermogravimetric analysis (TGA) was carried out on the 1H-Imidazolinium

    Hydrogen L-tartrate crystals and TGA spectrum was recorded in Nitrogen

    atmosphere between 50 and 500°C using NETZSCH STA 409 C/CD TGA

    unit. The recorded 1H-Imidazolinium Hydrogen L-tartrate is shown in

  • 55

    Figure 2.11. There is no weight loss between 50°C and 204°C. This indicates

    that there is no inclusion of water in the crystal lattice, which was used as the

    solvent for crystallization. The thermogram spectrum reveals that the major

    weight loss (around 92%) starts at 204.4°C and it continues up to 250°C. The

    nature of weight loss indicates the decomposition point of the material.

    However, below this temperature no weight loss is observed. In the DTA

    spectrum an irreversible exothermic peak observed around 204.4°C

    corresponds to the decomposition temperature of the material.

    Figure 2.11 TG and DTA curves of 1H-Imidazolinium Hydrogen

    L-tartrate

    2.7 SECOND HARMONIC GENERATION

    A quantitative measurement of the Second Harmonic Generation

    (SHG) conversion efficiency of 1H-Imidazolinium Hydrogen L-tartrate was

    made by the Kurtz and Perry powder technique (1968). The schematic of the

    experimental set up is shown in Figure 2.12. The finely powdered sample of

  • 56

    1H-Imidazolinium Hydrogen L-tartrate was densely packed between two

    transparent glass slides. A fundamental Laser beam of 1064 nm wavelength

    from an Nd: YAG (DCR11) laser was made to fall normally on the sample

    cell. The power of the incident beam was measured using a power meter. The

    transmitted fundamental wave was passed over a monochromator (Czerny

    turner monochromator) which separates 532 nm (second harmonic signal)

    from 1064 nm, and absorbed by a CuSO4 solution F1 which removes the

    1064 nm light. F2 is a BG-38 filter, which also removes the residual 1064 nm

    light. F3 is an interference filter with bandwidth of 4 nm and central

    wavelength 532 nm. The green light was detected by a photomultiplier tube

    (Hamamatsu R5 109, a visible PMT) and displayed on a storage oscilloscope

    (TDS 3052 B 500 MHz phosphor digital oscilloscope). KDP and Urea

    crystals were separately powdered to identical particle size and were used as

    reference materials in the SHG measurement. A bright green flash emission

    from the title sample was observed which indicates the NLO behavior of the

    material. The SHG of 1H-Imidazolinium Hydrogen L-tartrate crystal was

    found to be 75 mV and that of 95 mV for KDP.

    Figure 2.12 Experimental set up used for measuring the relative SHG

    efficiency

  • 57

    2.8 VICKER’S MICROHARDNESS STUDIES

    The mechanical characterization of 1H- Imidazolinium Hydrogen

    L-tartrate crystals has been done by microhardness testing at room

    temperature. Transparent 1H-Imidazolinium Hydrogen L-tartrate crystals free

    from cracks having the dimension of 3mm × 3 mm × 2 mm, with flat and

    smooth faces are chosen for the static indentation tests. The crystal was

    mounted properly on the base of the microscope. Now the selected faces have

    been indented gently by applying loads varying from 10 to 50 g for a dwell

    period of 3 second using Vickers diamond pyramid indenter attached to an

    incident researcher microscope. The indented impressions are pyramidal in

    shape. The shape of the impression is structure dependent, face dependent and

    also material dependent. The length of the two diagonals has been measured

    by a calibrated micrometer attached to the eyepiece of the microscope after

    unloading and the average is found out. For a particular load five

    well defined impressions were considered and the average of all the diagonals

    (d) was considered. The Vickers hardness numbers (Hv) have been calculated

    using the standard formula

    2

    1.8544v

    PH

    d= kg/mm2 (2.2)

    where P is the applied load in kg and d in mm. Crack initiation and materials

    clipping become significant beyond 50 g of the applied load. Hence hardness

    test could not be carried out above this load. Figure 2.13 shows the variation

    of Hv as a function of applied load ranging from 10 to 50 g. It is clear from

    the Figure 2.13 that Hv increases with increase in load (5 to 50 g). This is

    known as load dependent hardness and here its value is found to be

    approximately 50 kg/mm2. Such a phenomenon of dependence of

    microhardness of a solid on the applied load at low level of testing load is

  • 58

    known as indentation size effect (ISE). The observed increase in hardness

    with increasing load is usually termed as reverse indentation size effect

    (Ramesh Babu et al 2006).

    Figure 2.13 Plot between load and Hardness number

    2.9 CONCLUSION

    Bulk single crystals of 1H-Imidazolinium Hydrogen L-tartrate were

    grown by slow evaporation solution growth technique. The optical studies

    show the absence of absorption above 338 nm. The SHG efficiency is

    comparable to that of the standard KDP crystal. From FT-IR spectrum, the

    functional groups were identified. The occurrence of π-π* transition in the

    carboxyl group accounts for the nonlinearity in the title compound. The

    dielectric behaviour of 1H-Imidazolinium Hydrogen L-tartrate was analysed.

    Group theoretical analysis of 1H-Imidazolinium Hydrogen L-tartrate reveals

  • 59

    that there are 150 vibrational optical modes which are seen to decompose into

    Γ150 = 74A + 73B apart from three acoustic modes (A + 2B). The thermogram

    of 1H-Imidazolinium Hydrogen L-tartrate crystal recorded in the present

    work, reveals that the incipient melting occurs at 204.4°C. The hardness

    study enumerates that grown crystals are moderately harder substance. Based

    on these facts, it could be proposed that this material can be better

    accommodated for optical applications.

of 22/22
38 CHAPTER 2 GROWTH AND CHARACTERIZATION OF 1H-IMIDAZOLINIUM HYDROGEN L-TARTRATE SINGLE CRYSTALS 2.1 INTRODUCTION Nonlinear Optical (NLO) materials are of current research interest in materials science for their applications in second and third harmonic generation, optical bistability, laser remote sensing, optical disk data storage, laser driven fusion, medical and spectroscopic laser (Santhanu Bhattacharya et al 1994). Organic molecules possess large second order molecular polarizability (β) and more favorable physical properties like large optical damage threshold and large birefringence. L-tartaric acid is a chiral dihydroxycarboxylic acid and it is capable of initiating multidirectional hydrogen bonding (Aakeröy et al 1994). The salts of tartaric acid belong to an important class of materials because of their interesting physical properties such as ferroelectricity, piezoelectricity and nonlinear optical properties (Second Harmonic Generation). The L-tartaric acid analogs were incorporated into organic salts and their NLO properties were widely studied in recent experiments (Renuka Kadirvelraj et al 1998). The nonlinear optical (NLO) properties of some complexes of L-tartaric acid nicotinamide have attracted significant attention because organic components contribute specifically to the process of second
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