Date post: | 20-Mar-2023 |
Category: |
Documents |
Upload: | parvathisait87gmail |
View: | 0 times |
Download: | 0 times |
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)[email protected]
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