Metastable morphotropic phase boundary state in the multiferroic BiFeO3–PbTiO3V. Kothai, R. Prasath Babu, and Rajeev Ranjan Citation: Journal of Applied Physics 114, 114102 (2013); doi: 10.1063/1.4821511 View online: http://dx.doi.org/10.1063/1.4821511 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/114/11?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Electric field induced cubic to monoclinic phase transition in multiferroic 0.65Bi(Ni1/2Ti1/2)O3-0.35PbTiO3 solidsolution Appl. Phys. Lett. 105, 162901 (2014); 10.1063/1.4899058 Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1−x)Bi(Ni1/2Ti1/2)O3-xPbTiO3 solid solution: A Rietveld study J. Appl. Phys. 116, 044102 (2014); 10.1063/1.4891106 Multiferroism and enhancement of material properties across the morphotropic phase boundary of BiFeO3-PbTiO3 J. Appl. Phys. 115, 104104 (2014); 10.1063/1.4868319 Very high remnant polarization and phase-change electromechanical response of BiFeO3-PbTiO3 at themultiferroic morphotropic phase boundary Appl. Phys. Lett. 101, 172908 (2012); 10.1063/1.4764537 Effect of stress induced monoclinic to tetragonal phase transformation in the multiferroic (1-x)BiFeO3-xPbTiO3system on the width of the morphotropic phase boundary and the tetragonality J. Appl. Phys. 110, 084105 (2011); 10.1063/1.3647755

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

Metastable morphotropic phase boundary state in the multiferroicBiFeO3–PbTiO3

V. Kothai, R. Prasath Babu, and Rajeev Ranjana)

Department of Materials Engineering, Indian Institute of Science, Bangalore-560012, India

(Received 23 July 2013; accepted 2 September 2013; published online 19 September 2013)

Temperature-time study of the magnetoelectric multiferroic (1-x)BiFeO3-(x)PbTiO3 by x-ray

and electron diffraction on the reported morphotropic phase boundary (MPB) compositions

revealed that this MPB does not correspond to the equilibrium state. The MPB like state is

rather of metastable nature and arise due to kinetic arrest of metastable rhombohedral (R3c)

phase, along with the equilibrium tetragonal (P4mm) phase. The life time of the metastable R3c

nuclei is very sensitive to composition and temperature, and nearly diverges at x ! 0.27. The

MPB like state appears only if the system is cooled before the metastable R3c nuclei could

vanish. These findings resolve the long standing controversy with regard to seemingly erratic

phase formation behaviour reported by different groups and provides a rational basis for

developing genuine equilibrium MPB compositions in this system for better piezoelectric

properties. VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4821511]

I. INTRODUCTION

Ferroelectric systems exhibiting morphotropic phase

boundary (MPB) are of great scientific and technological in-

terest. MPB systems exhibit significantly enhanced piezo-

electric response and are used as actuators and transducers in

a wide variety of applications. In general, an MPB is charac-

terized by coexistence of two ferroelectric phases around a

composition induced ferroelectric-ferroelectric transition.1

For the widely used commercial piezoelectric, PZT, which is

a solid solution of PbTiO3 and PbZrO3, the MPB is charac-

terized by the coexistence of tetragonal and rhombohedral/

monoclinic phases.1,2 Though the theory of enhanced piezo-

response in the MPB systems is still being debated with one

school of thought emphasizing the importance of polariza-

tion rotation within a monoclinic phase3,4 and another school

of thought suggesting formation of nano-sized twins with

drastically reduced domain wall energy,5,6 recent few years

have also witnessed considerable emphasis on search for

new MPB systems. The thrust for new MPB systems is pri-

marily motivated by the need to replace the toxic lead-based

PZT. However, there are also specific needs to develop good

piezoelectric materials, which can work under relatively

harsh temperature environment, such as fuel modulation in

engines, space explorations, deep oil explorations, etc.7 The

ferroelectric system (1-x)BiFeO3-xPbTiO3 has been argued

as one of the potential candidate for the latter case since (i) it

has been reported to exhibit MPB, a feature desired for better

piezoelectric properties, and (ii) it exhibits high Curie point

(�700 �C).8–19 However, its potential as a high temperature

piezoelectric material has not been fully realized as yet, and

there seems to be a lack of understanding with regard to the

very nature of the reported MPB itself. Different research

groups have reported different composition range of MPB

for this system even for almost similar synthesis conditions.

Some authors have attributed this erratic behaviour to the

poor specimen quality.13 Very recently, we have demon-

strated that even experiments repeated under similar condi-

tion gave two different outcomes—sometimes, the sintered

pellet was found to be fragmented to powder; and on certain

occasions, it remained as a dense solid pellet after sintering.

Most importantly, it was invariably noticed that the pellet

consisted of R3cþP4mm phase mixture whereas the

powders were pure P4mm.19 A fundamental understanding

of this seemingly unpredictable phase formation behaviour

only for a certain composition range is highly called for as it

is also likely to be linked with the factor, which hinders the

realization of the interesting piezoelectric application envis-

aged for this MPB system. In a major step, in this work,

we have resolved the underlying phenomenon responsible

for this behaviour by carrying out a very systematic time-

temperature study by two complementary techniques—x-ray

and electron diffraction. The study proves the metastable na-

ture of the R3c phase for the reported MPB compositions.

The nuclei of this metastable phase survive well above the

Curie point. The occurrence of MPB like state is dependent

on whether or not the kinetic arrest of the metastable R3c

nuclei takes place while cooling. This fundamental under-

standing provides a sound basis for developing a logical

approach towards chemical designing of genuine (equilib-

rium) MPB compositions based on this system for better

piezoelectric properties.

II. EXPERIMENTAL

The solid solutions of (1�x) BiFeO3–(x) PbTiO3 with

x¼ 0.25 to x¼ 0.40 were prepared by conventional solid

state route using Bi2O3, PbO, Fe2O3, and TiO2 as precursors.

The milled powders were calcined at 800 �C for 2 h and the

disc of 10 mm dia and 1.5 mm thickness were sintered at 950

to 1020 �C in the alumina plate surrounded by the powders

of same composition to avoid the volatilization of PbO and

Bi2O3 and was closed with alumina crucible. The uncertaintya)rajeev@materials.iisc.ernet.in

0021-8979/2013/114(11)/114102/6/$30.00 VC 2013 AIP Publishing LLC114, 114102-1

JOURNAL OF APPLIED PHYSICS 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

in the phase formation is more in the MPB if the sacrificial

powder is not of the same composition and the pellet sizes

are different. To avoid this, all the samples were sintered

using the same composition as the environment and the size

was kept constant for all the compositions. The sintering

temperature was varied by 10 �C interval and the final sinter-

ing temperature was decided by the stability of the sample

without melting. At that temperature, the sample was

sintered at the longer time to check the stability of the dense

pellet and disintegration of the pellet. The room temperature

x-ray powder diffraction was carried out on XPERTPro,

PANalytical diffractometer, and the high temperature XRD

in the Bruker powder diffractometer (D8 Advance) using

CuKa radiation. Rietveld refinement was carried out using

FULLPROF program.20 Pseudo Voigt profile was considered

for the peak shape, the linear least square method was con-

sidered for the background correction, and the anisotropic

thermal parameters were refined for Bi and Pb. The composi-

tion of the samples was analyzed with Energy Dispersive x-

ray (EDX) Spectroscopy in FEI ESEM Quanta 200, operated

at 20KV. For TEM samples, the sintered pellets were thinned

down mechanically using SiC emery papers of different

grades (from P1000 to P4000) until 100 lm thickness. These

foils were annealed to remove surface residual stress at

600 �C for 10 h. Then, they were further thinned down to

form a hole with its edges thin enough for electron transpar-

ency by ion milling using Gatan Precision Ion Polishing

System (PIPS) with Ar ions impinging at angles of 4�

and 2�. High temperature in-situ TEM studies were carried

out in FEI-Tecnai F30 G2 microscope with a Gatan double

tilt heating stage at 300 kV accelerating voltage. The diffrac-

tion patterns and images were analyzed using Gatan Digital

microscope software.

III. RESULTS AND DISCUSSION

A. Phase formation behaviour with temperature andtime: X-ray diffraction study

Fig. 1 shows the XRD patterns of (1�x) BiFeO3-(x)

PbTiO3 at room temperature in the composition range

0.25� x� 0.40. Following literature, the sintering tempera-

ture was kept in the range 950–1020 �C for a maximum of

2 h. The XRD patterns reveal coexistence of rhombo-

hedral (R3c) and tetragonal (P4mm) phases in the range

0.25� x< 0.40. For sake of direct comparison, we provide a

list of the other relevant work reporting the MPB range of

this system in Table I. Except for Bhattacharjee et al.,13 who

reported the narrowest MPB range 0.27� x� 0.31, the

results shown in Fig. 1 are consistent with the other works.

In our previous study,19 we reported that on some occasions,

under identical synthesis conditions, some of the sintered

pellets became powder while others remained as solid after

sintering. It was also found that invariably the powder speci-

mens exhibited pure tetragonal and the pellets exhibited the

phase mixture of tetragonal (P4mm) and rhombohedral

(R3c). To understand the phenomenon better, we chose the

composition x¼ 0.29, which all the authors in the past have

agreed to be a MPB composition, and investigated the phase

formation behaviour as a function of heating time by fixing

the temperature at 970 �C. Fig. 2 shows the XRD patterns of

the specimen subjected to different heating duration at this

temperature. Both the phases survive up to 9 h of heating. As

shown in the inset of this figure, the relative volume fraction

of the tetragonal phase, obtained by Rietveld analysis of the

patterns, exhibits a gradual increase from 36% to 47% in this

duration. However, somewhere in between the 9th and the

10th h, the remaining 50% rhombohedral phase disappeared

almost suddenly making the specimen pure tetragonal. The

corresponding specimen was no more a pellet but was found

to be fragmented spontaneously into powder. This confirms

the metastable nature of the rhombohedral phase, which is

irreversibly lost after staying sufficiently long at high tem-

perature. Interestingly, when the temperature was increased

from 970 to 980 �C, i.e., merely by 10 �C, the time required

to complete transformation to the tetragonal phase got

reduced to 2 h. This experiment proves the extreme

FIG. 1. X-ray powder diffraction patterns of (1�x)BiFeO3-(x)PbTiO3 show-

ing coexistence of tetragonal and rhombohedral phases.

TABLE I. Morphotropic phase boundary range reported by different groups in the past in (1�x) BiFeO3-(x)PbTiO3.

Research group Sintering temperature/time MPB range (1�x)BiFeO3-xPbTiO3 Preparation method

Fedulov et al. (Ref. 8) 800–1000 �C/ 1 h x¼ 0.27–0.34 Solid state route

Woodward et al. (Ref. 11) 1000 and 1025 �C/2 h x¼ 0.3–0.4 Solid state route

Bhattacharjee et al. (Ref. 13) 900 �C/1 h (Annealed at 700 �C /10 h) x¼ 0.27–0.31 Solid state route

Zhu et al. (Ref. 12) 1000–1120 �C X¼ 0.20–0.40 Solid state route

Correas et al. (Ref. 18) 1050 �C X¼ 0.25–0.35 Mechanosynthesis

114102-2 Kothai, Babu, and Ranjan J. Appl. Phys. 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

sensitivity of this composition with regard to the stability of

the R3c phase as a function of temperature and time. The

effect of temperature and time for three other neighboring

compositions in the reported MPB range is shown in Fig. 3.

For the next higher composition, x¼ 0.30, at 980 �C, phase

coexistence is observed for 2 h heating and pure tetragonal

phase for 4 h. Lowering the temperature by mere 20 �C for

this composition resulted in the survival of the two phases up

to 4 h, and transformation to pure tetragonal in 6 h. For a

slightly lower composition, x¼ 0.275, the two phase nature

survived for 8 h even at a slightly higher temperature of

990 �C. It required a longer heating duration of 12 h at this

temperature to make the system pure tetragonal. For

x¼ 0.27, the phase coexistence survives until 16 h at this

temperature. These experiments were repeated several times

to check the reproducibility of the observations. The results

clearly suggest that the phase formation behaviour is very

sensitive to composition, temperature, and time around

x¼ 0.27. A small variation in temperature and time, which

most often is not given serious consideration, turn out be an

important factor with regard to this system in determining

the final phase formation behaviour, and is at the root of the

seemingly erratic phase formation behaviour reported in the

past.

In principle, one may suspect that due to the presence of

volatile elements, Pb and Bi, prolonged heating at higher

temperature may disturb the stoichiometry, and that the pres-

ence/absence of the MPB state may be associated with this

process. The likelihood of this scenario was examined by

compositional investigation on a representative composition,

x¼ 0.275 by EDX spectroscopy. For this composition, the

two phases R3cþ P4mm survive up to 8 h of heating at

990 �C and was found to be single phase P4mm after 12 h at

the same temperature. EDX analysis was accordingly carried

out on the specimens exhibiting R3cþP4mm phase coexis-

tence and that exhibiting pure P4mm phase. Figure 4 shows

the percentage of Bi from EDX at 30 different spots selected

at random for both the specimens. The sameness of the rela-

tive percentage of Bi for both the specimens at once proves

their overall compositional similarity. The same situation

was found for the other cations. The two phase (MPB like

state) and the single phase (pure tetragonal) formation is

therefore not due to alteration of the overall composition as a

result of different heating durations at high temperature.

B. Evidence of metastable R3c phase above the Curiepoint: Electron diffraction study

It may be mentioned that the temperatures under consid-

eration, discussed above, are well above the Curie point of

the system. The system exhibits cubic phase for all the com-

positions above 800 �C. The question which arises is that

what has staying in the deep cubic temperature region to do

with the occurrence or disappearance of rhombohedral phase

FIG. 3. X-ray powder diffraction patterns of (1�x)BiFeO3-(x)PbTiO3 show-

ing the temperature (�C)—time (h) combination corresponding to coexis-

tence of phases and vanishing of the metastable rhombohedral phase for

three compositions.

FIG. 2. XRD patterns of 0.71BiFeO3-0.29PbTiO3 sintered at 970 �C for dif-

ferent durations. The inset shows the variation of the rhombohedral and the

tetragonal volume fractions with sintering time.

FIG. 4. Percentage of Bi from EDX at 30 different random spots.

114102-3 Kothai, Babu, and Ranjan J. Appl. Phys. 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

at room temperature. Since the overall composition of the

MPB and the pure tetragonal states are similar (Fig. 4), one

trivial explanation which may be advanced is that for shorter

heating time the diffusion of the chemical species may not

be complete and may lead to Bi-rich and Bi-deficient

regions. In such a scenario, the observed two phases (R3cþP4mm) may be speculated to arise due to chemical hetero-

geneity. While one may be tempted to accept the plausibility

of this argument for the specimens exhibiting different

results when heated for 2 h and 4 h as is the case for x¼ 0.30

and 0.29, this logic cannot be applied to the compositions

x¼ 0.275 and 0.27, which exhibit two phase even after heat-

ing for 8 h and 16 h, respectively, at 980 �C. More so, if a

process is primarily limited by insufficient diffusion of the

chemical species, and that if the resulting chemical heteroge-

neity is to be associated with the formation of the two-phase

MPB like state, there is no special reason as to why the ho-

mogenization time by diffusion process should increase dras-

tically from 2 h to more than 16 h for a mere small increase

in the Bi composition from 71 to 73 mol. %. These results

therefore do not favor the possible stabilization of the R3c

phase due to limited mobility of the chemical species. The

other possibility is that although the system exhibits a cubic

phase on a global length scale, tiny rhombohedral nuclei

may be present even in this phase. These nuclei would grow

on cooling along with the tetragonal phase leading to the

MPB like state.

To capture localized R3c regions at high temperatures,

in-situ high temperature electron diffraction experiment was

carried out on the pellets of x¼ 0.27 and x¼ 0.35. XRD

study have shown that at room temperature, the pellets of

x¼ 0.27 exhibits majority rhombohedral phase whereas

x¼ 0.35 exhibits a majority tetragonal phase (�90%).19 The

samples were heated continuously and TEM images and

selected area diffraction pattern (SADP) of the selected

regions were captured at different temperatures. Figures 5(a)

and 5(b) show the bright field (BF) image and the corres-

ponding (1–10) rc pseudo cubic zone axis selected area dif-

fraction pattern of the same region of the x¼ 0.27 specimen

at room temperature. For sake of convenience, the diffracted

spots are indexed with pseudocubic setting of rhombohedral

phase in Figure 5(b). Due to the R3c structure of the rhombo-

hedral phase, it was easy to identify its presence through the

characteristic superlattice 1=2{hkl}rc spots.11,21,22 These

superlattice reflections are generally considered to arise due

to the a-a-a- octahedral tilt.23,24 It is evident from Figs.

5(c)–5(e) that the intensity of the superlattice spots becomes

weak with increasing temperature. Most importantly, these

spots could still be seen at 800 �C, a temperature which is

well above the Curie point of this composition. The XRD

pattern shown in Fig. 5(f) shows all the Bragg peaks to be

singlet at 660 �C for x¼ 0.27 confirming the cubic state on

the global scale. This result conclusively proves that the

rhombohedral nuclei are present well above the Curie point

of the system.

Figures 6(a) and 6(b) show the BF image and SADP of

the same region at room temperature of x¼ 0.35. At 200 �C(Fig. 6(c)), additional spots around the main spots become

visible. These spots correspond to the appearance of an

intermediate tetragonal (T2) phase, the tetragonality of which

has been reported to be comparatively small as compared to

that of the majority room temperature tetragonal (T1)

phase.19 The intensity of the new spots corresponding to the

T2 phase increases considerably at 500 �C suggesting consid-

erable increase in the fraction of the T2 phase (Fig. 6(d)).

Concomitantly, the intensity of the superlattice spots, charac-

teristic of the R3c phase, decreases with increasing tempera-

ture. These observations are in good agreement with our

earlier neutron diffraction study of this composition.19

Interestingly, though the XRD pattern at 650 �C of this com-

position shows a cubic phase, the superlattice peaks corre-

sponding to the R3c phase is still visible at 700 �C (Fig. 6(f))

in the electron diffraction pattern, confirming again the pres-

ence of this phase above the Curie point of this composition.

The gradual vanishing of the intensity of the superlattice

spots of the R3c phase region in the cubic phase region is in-

dicative of the fact that this phase is likely to survive as clus-

ters (nuclei) above the upper temperature limit of our in-situTEM study. With regard to the occurrence of the R3c phase

at room temperature, what matters is life time of these

nuclei. The different powder x-ray diffraction patterns in

Fig. 3 at room temperature for specimens treated at slightly

different temperature and time can now be understood on the

FIG. 5. (a)Bright field image of x¼ 0.27. Selected Area Diffraction Pattern

of same region at (b) room temperature, (c) 450 �C, (d) 650 �C, and (e)

800 �C where thick arrows show the super lattice reflections and (f) X-ray

powder diffraction pattern at 30 �C and 660 �C.

114102-4 Kothai, Babu, and Ranjan J. Appl. Phys. 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

basis of the life time of the R3c nuclei at any given tempera-

ture. If the system is cooled before the R3c nuclei vanish

completely at that temperature, these nuclei would grow on

cooling and the R3c phase will be observed, otherwise not.

For example, for x¼ 0.30, the R3c nuclei disappears after 4

h at 980 �C, whereas it is still present in the 4th h at 960 �Cand takes a little longer (6 h) for complete disappearance at

this temperature. The erratic phase formation behaviour

reported in the past for a certain composition range around

x¼ 0.27 can now be understood in terms of these subtle

intrinsic features of the system. The reported MPB range

therefore does not represent the equilibrium state of the sys-

tem. The system may rather be termed as metastable MPB as

one of the coexisting phase, R3c, is metastable in nature.

The non realization of the anticipated good piezoelectric

properties is most likely to be related to this metastable na-

ture of the MPB. In equilibrium MPB systems, such the

PZT, the free energies of the coexisting phases are very close

to each other and are separated by small potential hill.25,26

For such systems, electric field can induce transformation

from one equilibrium ferroelectric phase to the other and the

system exhibit considerably enhanced piezoelectric

response.27 Fortunately, for the BiFeO3-PbTiO3 system,

since the life time of the R3c nuclei tend to diverge for

x!0.27, the genuine MPB, if any, must be very close to this

composition. Alternatively, the equilibrium MPB state can

be stabilized by suitable chemical modifications of the meta-

stable MPB compositions. Such modified systems are likely

to provide high piezoelectric response.

IV. CONCLUSIONS

In conclusion, a systematic temperature-time study of

the reported morphotropic phase boundary compositions of

the BiFeO3-PbTiO3 system by x-ray and electron diffraction

revealed the metastable nature of the rhombohedral (R3c)

phase. The nuclei of the metastable R3c phase were found to

be present well above the Curie point, and its life time is

highly sensitive to small change in temperature and composi-

tion. The MPB like state arises due to kinetic arrest of these

metastable nuclei, otherwise the equilibrium state of the sys-

tem exhibits pure tetragonal phase. This fundamental under-

standing resolves the longstanding debate with regard to the

erratic phase formation behaviour of this interesting multi-

ferroic system. The study also suggests the necessity to

induce equilibrium MPB state, perhaps by suitable chemical

modification of the metastable MPB compositions, if the sys-

tem’s potential as an interesting piezoelectric material is to

be achieved.

ACKNOWLEDGMENTS

R.R. gratefully acknowledges the financial support from

Department of Science and Technology, Govt. of India and

the Council of Scientific and Industrial Research, India.

Authors would like to acknowledge the experimental facility

in AFMM centre, IISc, Bangalore.

1B. Jaffe, W. R. Cook, and H. Jaffe, Piezoelectric Ceramics (Academic

Press, London, 1971).2B. Noheda, D. E. Cox, G. Shirane, J. A. Gonzalo, L. E. Cross, and S.-E.

Park, Appl. Phys. Lett. 74, 2059 (1999).3H. Fu and R. E. Cohen, Nature (London) 403, 281 (2000).4D. Vanderbilt and M. H. Cohen, Phys. Rev. B 63, 094108 (2001).5Y. M. Jin, Y. U. Wang, A. G. Khachaturyan, J. F. Li, and D. Viehland,

J. Appl. Phys. 94, 3629 (2003).6Y. U. Wang, Phys. Rev. B 76, 024108 (2007).7See http://solarsystem.nasa.gov/planets/profile.cfm?Object=Venus&Display

=Facts&System=Metric for the solar system exploration.8S. A. Fedulov, P. B. Ladyzhinskii, I. L. Pyatigorskaya, and Yu. N.

Venevetsev, Sov. Phys. Solid State 6, 375 (1964).9R. T. Smith, G. D. Achenbach, R. Gerson, and W. J. James, J. Appl. Phys.

39, 70 (1968).10V. V. S. Sai Sunder, A. Halliyal, and A. M. Umarji, J. Mater. Res. 10,

1301 (1995).11D. I. Woodward, I. M. Reaney, R. E. Eitel, and C. A. Randall, J. Appl.

Phys. 94, 3313 (2003).12W.-M. Zhu, H.-Y. Guo, and Z.-G. Ye, Phys. Rev. B 78, 014401 (2008).13S. Bhattacharjee, S. Tripathi, and D. Pandey, Appl. Phys. Lett. 91, 042903

(2007).14R. Ranjan and A. Raju, Phys. Rev. B 82, 054119 (2010).15S. Bhattacharjee, K. Taji, C. Moriyoshi, Y. Kuroiwa, and D. Pandey, Phys.

Rev. B 84, 104116 (2011).16R. Ranjan, V. Kothai, A. Senyshyn, and H. Boysen, J. Appl. Phys. 109,

063522 (2011).17S. Bhattacharjee and D. Pandey, J. Appl. Phys. 110, 084105 (2011).18C. Correas, T. Hungr�ıa, and A. Castro, J. Mater. Chem. 21, 3125 (2011).19V. Kothai, A. Senyshyn, and R. Ranjan, J. Appl. Phys. 113, 084102

(2013).

FIG. 6. (a) Bright field image of x¼ 0.35. Selected Area Diffraction Pattern

of same region at (b) room temperature, (c) 200 �C, (d) 500 �C, and (e)

700 �C where thick arrows show the super lattice reflections and (f) X-ray

powder diffraction pattern at 30 �C and 660 �C.

114102-5 Kothai, Babu, and Ranjan J. Appl. Phys. 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28

20J. Rodrigues-Carvajal, “FULLPROF-2000,” in A Rietveld Refinement andPattern Matching Analysis Program, Laboratoire Leon Brillouin (CEA-

CNRS), France.21I. M. Raney, E. L. Colla, and N. Setter, Jpn. J. Appl. Phys., Part 1 33, 3984

(1994).22H. Huang, L. M. Zhou, J. Guo, H. H. Hng, J. T. Oh, and P. Hing, Appl.

Phys. Lett. 83(18), 3692 (2003).

23A. M. Glazer, Acta Crystallogr. B 28, 3384 (1972).24A. M. Glazer, Acta Crystallogr. A 31, 756 (1975).25D. Damjanovic, Appl. Phys. Lett. 97, 062906 (2010).26L. Bellaiche, A. Garc�ıa, and D. Vanderbilt, Phys. Rev. Lett. 84, 5427

(2000).27D. Maurya, A. Pramanick, K. An, and S. Priya, Appl. Phys. Lett. 100,

172906 (2012).

114102-6 Kothai, Babu, and Ranjan J. Appl. Phys. 114, 114102 (2013)

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

130.88.99.226 On: Fri, 31 Oct 2014 13:37:28