Dielectric and polarized Raman spectroscopic studies on 0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3 single crystalK. K. Mishra, A. K. Arora, S. N. Tripathy, and Dillip Pradhan Citation: Journal of Applied Physics 112, 073521 (2012); doi: 10.1063/1.4757958 View online: http://dx.doi.org/10.1063/1.4757958 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/112/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Structural change in polar nanoregion in alkali niobate added Pb(Zn1/3Nb2/3)0.95Ti0.05O3 single crystal and itseffect on ferroelectric properties J. Appl. Phys. 112, 074109 (2012); 10.1063/1.4757620 Micro-Raman study of the microheterogeneity in the M A-M C phase transition in 0.67PbMg1/3Nb2/3O3-0.33PbTiO3 single crystal J. Appl. Phys. 109, 083517 (2011); 10.1063/1.3574666 Infrared and Raman spectroscopy of [ Pb ( Zn 1/3 Nb 2/3 ) O 3 ] 0.92 –[ PbTiO 3 ] 0.08 and [ Pb ( Mg 1/3 Nb 2/3) O 3 ] 0.71 –[ PbTiO 3 ] 0.29 single crystals J. Appl. Phys. 93, 933 (2003); 10.1063/1.1528274 Diffuse Neutron Scattering Study of Relaxor Ferroelectric (1−x)Pb(Zn1/3Nb2/3)O3xPbTiO3 (PZNxPT) AIP Conf. Proc. 626, 99 (2002); 10.1063/1.1499557 Dielectric and piezoelectric properties of the Mn-substituted Pb ( Zn 1/3 Nb 2/3 ) O 3 – PbTiO 3 single crystal J. Appl. Phys. 91, 4515 (2002); 10.1063/1.1459101

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

Dielectric and polarized Raman spectroscopic studies on0.85Pb(Zn1/3Nb2/3)O3-0.15PbTiO3 single crystal

K. K. Mishra,1,a) A. K. Arora,1 S. N. Tripathy,2 and Dillip Pradhan2

1Condensed Matter Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India2Department of Physics, NIT Rourkela, Rourkela 769008, India

(Received 4 July 2012; accepted 10 September 2012; published online 10 October 2012)

Tetragonal-cubic phase transition has been investigated in relaxor-ferroelectric 0.85Pb(Zn1/3Nb2/3)

O3-0.15PbTiO3 single crystal using dielectric and Raman spectroscopy. A detailed analysis of the

dielectric data suggests that the transition is of second order. In the tetragonal phase (P4mm), all the

modes predicted by group theory were found in the Raman spectra and were assigned based on the

symmetry and polarization configuration. Frequencies of several modes were found to disappear

while a few modes exhibited discontinuous change across the phase transition temperature TC

�473 K. While in the high temperature cubic phase (Pm�3m) no first order Raman spectrum is

expected, the presence of several Raman peaks at elevated temperature suggests substitutional

disorder causing the appearance of symmetry-forbidden Raman bands. The line-width of A1(TO)

mode at 273 cm�1 shows anomalies across TC and the intermediate temperature T*. Furthermore,

based on the temperature dependence of total integrated intensities of all the modes in the polarized

and depolarized spectra, the Burns temperature TB, T*, and TC are identified at 650, 525, and 473 K,

respectively. VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757958]

I. INTRODUCTION

Perovskite-type (ABO3) relaxor ferroelectric materials

have attracted attention of researchers because of their tech-

nological applications and also from fundamental point of

view.1–4 Their behaviour is characterized by high dielectric

constant and broad frequency dependent dielectric maximum

with temperature. In the case of lead-based ferroelectrics the

cations, in the high temperature paraelectric phase, are

expected to move freely among the available equivalent off-

center positions in the unit cell and hence the crystal has an

average Pm�3m structure.5 The occupation of the B-site by

cations of different atomic radii and valencies can lead to the

formation of chemically ordered nano-regions with Fm�3msymmetry.6–8 Therefore, in the paraelectric state the symme-

tries of the chemically ordered and disordered regions are

Fm�3m and Pm�3m, respectively.9,10 Upon cooling, the corre-

lation between the off-center cations gives rise to the forma-

tion of polar nano regions (PNRs). The temperature

evolution of PNRs is characterized by three temperatures.11

Below the Burns temperature TB, the nucleation of PNRs

begins. In addition, at this temperature, the lifetime of PNRs

exceeds the period of the optical phonon and hence these are

in quasi-dynamic state.11 At an intermediate temperature T*,

the originally formed PNRs coalesce to form large PNRs or

in other words, the T* marks the appearance of static or per-

manent correlations of the off-center ion displacements.11,12

Finally at freezing temperature Tf, the off-center ions are

arrested in one position. PNRs become static at Tf in the case

of a canonical relaxor. On the other hand, other relaxors,

which develop long-range ferroelectric order,12 undergo a

transition to normal ferroelectric state at the Curie tempera-

ture TC. (1� x)Pb(Zn1/3Nb2/3)-x(PbTiO3) ((1� x)PZN-xPT)

relaxor ferroelectrics are known to possess excellent piezo-

electric and dielectric properties.13 This solid solution

belongs to the family of Perovskite structure. The sublattice

A is occupied by Pb2þ ions and the B-site is randomly occu-

pied by Zn2þ, Nb5þ, and Ti4þ ions. It may be pointed out

that the individual components of the solid solution are dif-

ferent in their dielectric behaviour. PZN is a relaxor ferro-

electric and it undergoes a phase transition from high

temperature cubic to rhombohedral phase at low temperature

with an intermediate relaxor state consisting of PNRs em-

bedded in a non-polar matrix.14,15 On the other hand, PT is a

well known classical ferroelectric that exhibits a cubic to tet-

ragonal phase transition. The doping of PT in PZN influences

the structural and relaxor properties.9,16 The phase diagram

of the (1� x)PZN-xPT shows a sequence of structural phases

with temperature and the composition x of PT. For x� 8%

the crystals show rhombohedral symmetry whereas for

x¼ 11%–15%, crystals are found to be in tetragonal phase

with lattice anisotropy increasing with x. For x¼ 15%, which

is located away from the morphotropic phase boundary

(MPB), the system exhibits tetragonal–cubic phase transition

around 490 K16 and possesses relaxor ferroelectric character.

Raman spectroscopy is known to be a sensitive tech-

nique for studying phase transitions and short-range ordering

in Perovskite ferroelectric crystals.10,17–19 Phonon anomalies

induced by temperature changes are associated with phase

transitions.17–21 Furthermore, it has the advantage that light

couples directly with the ferroelectric order parameter

(polarization) and is therefore useful in study of PNRs dy-

namics also.11,12,22–24 Raman spectroscopic studies have

been reported for x¼ 4.5%,9 which is on the rhombohedral

side of the phase diagram and also for x¼ 8%,25,26 9%,27

and 10%,10 which are at the MPB. To our knowledge, polar-

ized Raman study on PZN-PT for a composition, which is on

a)Author to whom correspondence should be addressed. Electronic mail:

karuna_phy05@yahoo.co.in.

0021-8979/2012/112(7)/073521/7/$30.00 VC 2012 American Institute of Physics112, 073521-1

JOURNAL OF APPLIED PHYSICS 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

the tetragonal side of phase diagram has not been reported

across tetragonal-cubic phase transition. Since the increase

in Ti content influences the structural and relaxor behav-

iour,9,11 the phonon spectra are also expected to be modified.

Furthermore, it is of interest to examine the differences in

the phonon behaviours of solid solutions near and away from

MPB. Such a study on a broad compositional range is

expected to improve the understanding of PNRs dynamics.

The aim of the present work is to study the tetragonal-cubic

phase transition and the dynamical aspects of PNRs in

relaxor state in 0.85PZN-0.15PT using dielectric and polar-

ized Raman spectroscopy in the temperature range 298–

873 K. Single crystals were synthesized by flux method and

relaxor-like behaviour was examined using dielectric

spectroscopy.

II. EXPERIMENTAL

Transparent and yellow color single crystals of

0.85PZN-0.15PT were grown by flux method with Pb3O4 as

flux. The charge and flux were taken in 40(PZN-PT):60

Pb3O4 wt. %. The crystals were grown by cooling from 1473

to 1203 K at a rate of 0.8 K/h and then from 1203 K to room

temperature at a rate of 300 K/h. The Perovskite tetragonal

(P4mm) phase was confirmed using x-ray powder diffraction

(XRD) analysis. The typical sample dimensions were

3� 2� 0.5 mm3. The grown single crystals were found to be

oriented in [100] plane from Laue pattern. The energy dis-

persive x-ray analysis of the sample was carried out using a

scanning electron microscope (CARL ZEISS, SUPRA 55).

The surfaces were polished to optical quality. For dielectric

measurement, the (100) faces of the single crystal were elec-

troded with silver paste. The dielectric parameters (capaci-

tance and dissipation factor) were measured in the frequency

range 2 kHz to 1 MHz using a computer-controlled LCR me-

ter/impedance analyzer (PSM: N4L (Model: 1735, UK)) in

the temperature range 300–585 K. Raman spectra were

recorded using a Ranishaw micro-Raman spectrometer

(model InVia) equipped with a Leica microscope and a

20� long-working distance objective. The measurements

were conducted in backscattering geometry using the

514.5 nm line of an Ar-ion laser. The spectrometer resolution

for 1800 l/mm grating was �1.5 cm�1. The in situtemperature-dependent measurements were carried out using

a Linkam heating-cooling stage ensuring a temperature sta-

bility of 60.1 K. Data acquisition time and the laser power

were adjusted for obtaining a good signal to noise ratio.

Polarized Raman spectra were measured upon heating from

room temperature to 873 K in X(YY)X0 (V-V) and X(YZ)X0

(V-H) scattering geometries (Porto’s notation), where X, Y,

and Z are parallel to the tetragonal [100], [010], and [001]

crystallographic directions, respectively. The spectra were

fitted to Lorenzian line shapes to determine the peak posi-

tions, full widths at half maximum (FWHM), and integrated

intensities, using PEAKFIT software (JANDEL).

III. RESULTS AND DISCUSSION

All the peaks of the x-ray diffraction pattern of the pow-

dered crystals of PZN-PT could be indexed to the tetragonal

crystal system with space group P4mm, with lattice parame-

ters a¼ 4.0165(6) A and c¼ 4.1027(9) A. These lattice pa-

rameters are in good agreement with the reported phase

diagram data on (1� x)PZN-xPT,16 suggesting that the

doped-Ti composition in the single crystal is x� 15%, well

within the expected stoichiometry of PZN-PT. Energy dis-

persive x-ray analysis on single crystal confirmed the pres-

ence of all the cationic elements in agreement with expected

stoichiometry within experimental error. Figure S1 (supple-

mentary material38) shows the diffraction pattern and the

EDAX spectrum.

A. Dielectric spectroscopy

Figure 1(a) shows the variation of dielectric permittivity

(er) with temperature at different frequencies. One can see

that er decreases with increasing frequency. This is the typi-

cal behavior of polar dielectric material.28 The relative

dielectric permittivity rises slowly with the increase in tem-

perature up to 450 K and then it suddenly increases to its

maximum value at Tm� 480 K. After reaching the maximum

value, it decreases monotonically with rise in temperature.

Furthermore, the dielectric peaks observed around

FIG. 1. (a) Temperature dependence of the dielectric constant (er) of PZN-

PT single crystal measured at different frequencies and (b) temperature de-

pendence of the dielectric loss (tan d) of PZN-PT single crystal measured at

different frequencies. Vertical dashed lines correspond to tetragonal-cubic

transition temperature.

073521-2 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

Tm� 480 K exhibit a clear but weak frequency dispersion.

This suggests that the system exhibits weak relaxor behav-

iour. For this PZN-PT composition, the tetragonal to cubic

phase transition was found to occur at a temperature close to

Tm.16 Thus, the dielectric anomaly observed around Tm could

be attributed to the ferroelectric to paraelectric phase transi-

tion (i.e., tetragonal-cubic phase). Figure 1(b) shows the tem-

perature dependence of tan d at selected frequencies. Two

peaks can be seen in the temperature range of investigation.

The first peak is observed between 350 and 425 K and the

second around 480 and 490 K. The first peak of the tan dshifts towards the high temperature side and the broadening

of the peak increases with increase in frequency. The second

peak corresponds to the ferroelectric transition, which also

manifested as a peak in er versus temperature plot. In order

to get an idea about the order of the phase transition, the re-

ciprocal of permittivity as a function of temperature has been

plotted at a selected frequency of 100 kHz and is shown in

Fig. 2. The effect of interfacial capacitance (which often

occurs at low frequencies) of the dielectric material was

avoided by selecting a high frequency (i.e., 100 kHz). The

plot of 1/er versus T shows different slopes below and above

the phase transition temperature. The corresponding deriva-

tive n¼ d/dT(1/er) (Fig. 2) has been argued to give informa-

tion about the order of phase transition and the transition

temperature.29 The temperature at which n¼ 0 corresponds

to the ferroelectric to paraelectric transition temperature,

which is found to be Tm in the present case. At low tempera-

ture (T< 450 K), n (��1.6� 10�6) remains temperature in-

dependent representing the ferroelectric state, and at high

temperature (T> 550 K) also n (�2.65� 10�6) remains inde-

pendent of temperature, which corresponds to paraelectric

state. In the neighborhood of transition temperature Tm, the

derivative value drops from 1.34� 10�6 (505 K) to

�2.85� 10�6 (475 K). The change in the derivative ratio is

found to be ��2.12 which is in an agreement with that

expected for a second order phase transition.29,30

B. Polarized Raman spectroscopy

The ambient tetragonal ferroelectric phase of PZN-PT

belongs to the space group P4mm. The irreducible representa-

tion of optical phonons in this phase is Uopt¼ 3A1þ 4EþB1,

where the A1 and E modes are both Raman and infrared

active, whereas the B1 mode is only Raman active. The

Raman tensors associated with these modes are

A1ðZÞ :

a 0 0

0 a 0

0 0 b

264

375; EðXÞ :

0 0 e

0 0 0

e 0 0

264

375;

EðYÞ :

0 0 0

0 0 e

0 e 0

264

375; B1 :

c 0 0

0 �c 0

0 0 0

264

375;

where X, Y, and Z indicate the polarization of the phonon

modes. The Raman modes allowed for [100] oriented single

crystal in X(YY)X0 scattering geometry are A1(TO)þB1

and E(TO) in X(YZ)X0 configuration. Figure 3(a) shows the

unpolarized Raman spectra measured at different tempera-

ture. At room temperature, a total of five prominent Raman

peaks and three shoulders are discernible in the frequency

range 90–1000 cm�1. By analysing the spectra using PEAKFIT,

11 modes could be identified. Figures 3(b) and 3(c) show the

polarized Raman spectra in V-V and V-H geometries at dif-

ferent temperatures, respectively. Here, we have presented

the reduced Raman intensity IR after correcting for the effect

of temperature so that the intensity changes can be compared

without the influence of thermal population factor, which is

given by IR ¼ IðxÞ=ðe�hx=kBT � 1Þ þ 1, where I(x) corre-

sponds to the measured Raman intensity and 1=ðe�hx=kBT

�1Þ þ 1 is the Bose-Einstein phonon population factor. The

Raman spectra were found to be broad at ambient tempera-

ture. The broad nature of the Raman modes has been recently

argued to arise due to substitutional disorder at cation site.17

At elevated temperature, the spectra broaden further and the

intensities are found to reduce as expected.

In order to study the dramatic changes caused by the

influence of temperature, a quantitative analysis of the

changes in the Raman spectra is required. This can be

achieved only when the peak positions, line-widths, and

intensities of the modes are precisely obtained using curve

fitting. Hence the reduced spectra were fitted to multi-

Lorenzians using the PEAKFIT program. In the context of num-

ber of peaks used for fitting the spectrum for a given temper-

ature, it is important to point out that although it is always

possible to fit more number of peaks to a given spectrum, we

adopted a strategy to use the minimum number of peaks that

yield a good fit. If one uses more number of modes than

required, it leads to large standard errors and strong correla-

tions in fitted parameters.19 The fitted parameters obtained

from unpolarized Raman spectra were used to ascertain the

positions and widths of the weak and poorly resolved peaks

of the V-V and V-H spectra.31 The fitted Raman peaks in the

V-V geometry at 298 and 713 K as a representative example

are shown in Fig. 4. At 298 K, ten modes could be identified

at 105, 204, 272, 419, 504, 604, 728, 760, 788, and

809 cm�1, respectively. On the other hand at 713 K, modes

at 105, 204, 419, 504, 728, and 809 cm�1 could not be identi-

fied and hence only four modes survived at this temperature.

Similarly, Fig. 5 shows the fitted Raman peaks at 298 K andFIG. 2. Temperature dependence of the inverse of dielectric constant (1/er)

and its T-derivative (n) for 100 kHz data.

073521-3 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

713 K in the VH geometry. At 298 K, seven modes at 176,

273, 307, 416, 530, 614, and 776 cm�1 are found whereas at

713 K, the modes at 416 and 614 cm�1 could not be found.

Less number of modes at high temperature in both the geo-

metries could be due to either insufficient intensity of weak

modes or transformation to the higher symmetry cubic phase.

The modes in higher temperature phase will be discussed

later. The Raman modes in the ambient temperature

FIG. 4. Multi-Lorenzian peak fitting of reduced Raman spectra at (a) 298 K

and (b) 713 K in V-V geometry.

FIG. 3. Raman spectra at different temperatures (a) unpolarized, and in (b) V-V and (c) V-H polarization geometries after correcting for thermal population

factor.

FIG. 5. Multi-Lorenzian peak fitting of reduced Raman spectra at (a) 298 K

and (b) 713 K in V-H geometry.

073521-4 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

tetragonal phase have not been assigned yet. Here, we pres-

ent the observed mode frequencies and their assignments in

both the geometries in Table I. The unassigned weak modes

are possibly due to polarization leakage.

Figure 6 shows the dependences of mode frequencies on

temperature in both polarized and depolarized geometries.

One can see that in the V-V geometry, modes at 419 and

504 cm�1 could not be followed at high temperature. Note

that disappearance of the modes at 105 and 204 cm�1 (Fig.

6(a)) at �473 K, as the sample undergoes the structural phase

transition. Similarly, the mode at 416 cm�1 in the V-H geom-

etry (Fig. 6(b)) is also found to vanish at �473 K. In addi-

tion, the modes at 273 and 760 cm�1 in V-V (Fig. 6(a)) and

those at 176 and 776 cm�1 in V-H (Fig. 6(b)) geometries

show a discontinuous change at �473 K. It may be men-

tioned that the mode disappearance, mode broadening, and

discontinuous change in mode frequencies are typical for

Perovskite ferroelectrics undergoing a phase transition.18,25

Therefore, the present observations suggests that the system

undergoes a tetragonal to cubic phase transition at �473 K,

which is close to the transition temperature reported from

XRD measurement16 as well as the dielectric results dis-

cussed earlier.

Figures 4(b) and 5(b) show the Raman spectra in high

temperature cubic phase. Appearance of Raman spectra in

high temperature cubic phase could be due to two reasons:

(a) disordered activated symmetry-forbidden scattering and/

or (b) existence of ordered nano-clusters of cubic Fm�3msymmetry in an over-all host of average cubic Pm�3m. From

group theoretical analysis, the total irreducible representation

of optical phonons in the cubic Pm�3m phase is10,17

Uopt¼ 3F1uþ F2u, where F1u is infrared active, and F2u is

inactive both in Raman and infrared (silent mode). These

modes can be correlated to those expected from the tetrago-

nal (P4mm) phase. A1 (R, IR) and E (R, IR) modes of tetrag-

onal phase give rise to F1u (IR) and that of B1 (R) and E (R,

IR) modes merge to give F2u silent mode. Thus, none of

these modes are Raman active in the cubic phase. Substitu-

tional disorder at B-cation site can lead to breakdown of

Raman selection rule causing the appearance of Raman

bands in the high temperature cubic phase. Thus, the spectra

in this phase are likely to have large contribution from the

phonon density of states.19 It can be mentioned here that the

zone center and other high symmetry points in the Brillouin

zone make significant contribution to the phonon density of

states. Therefore, in principle all the phonons, whether

Raman active or not, can contribute to the disorder-activated

Raman scattering.

As mentioned earlier, Raman modes can also arise from

chemically ordered nano-regions of double Perovskite struc-

ture (Fm�3m) dispersed in a disordered matrix with an aver-

age single Perovskite structure (Pm�3m). In view of the

length scale of sensitivity (a few nm)12 of Raman scattering,

ordered nano-regions can in principle give rise to Raman

spectrum. In fact in many similar substituted systems, it has

been argued that the chemically ordered nano-regions give

rise to Raman bands.20,32 It has been further argued that the

TABLE I. Raman mode frequencies (cm�1) and their assignments in

0.85PZN-0.15PT single crystal in different polarization configurations.

X(YY)X0A1(TO)þB1 X(YZ)X0E(TO)

105.9(9) A1(TO) …

… 176.2(7) E(TO)

204(2) …

272.7(4) A1(TO) 273(1) E(TO)

… 307(21)

419(2) 416.4(8)

504(4) …

… 530.8(4) E(TO)

604.7(5) B1 614(2)

728(4) …

760(2) …

788(1) A1(TO) 776.4(4) E(TO)

809(4) …

FIG. 6. Dependence of Raman mode fre-

quencies on temperature in (a) V-V and

(b) V-H geometries. Vertical dashed

lines correspond to tetragonal-cubic

transition temperature.

073521-5 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

PZN and Pb(Mg1/3Nb2/3)O3 (PMN), when added with mod-

erate amount of PT, do not disturb the cubic ordered struc-

ture (Fm�3m).9,10 A strong mode at �788 cm�1 has been

found in the Raman spectra of several Pb-based relaxors

such as 0.9PZN-0.1PT,10 PZN,11 PbSc0.5Nb0.5O3 and

PbSc0.5Ta0.5O3 (PST),33 Pb(Mg1/3Nb2/3)O3,34 and doped-

PST.35 It is likely that the Raman scattering in 0.85PZN-

0.15PT could also have contributions from the ordered

Fm�3m regions. The optical phonons in this phase are

Uopt¼A1gþEgþ 2F2gþ F1gþ 4F1uþ F2u.11,36 In this phase,

A1g, Eg, and 2F2g Raman active non-polar phonons are

expected. According to the selection rules, A1g and Eg modes

appear in X(YY)X0 geometry and the F2g modes are allowed

in X(YZ)X0 geometry. However, all these modes continue to

have correspondence with those of the tetragonal phase.

Therefore, it is more appropriate to attribute the Raman

bands in the cubic phase to symmetry-forbidden scattering.

The temperature dependence of total integral intensity

has been argued to be useful in determining the characteristic

temperatures in the evolution of PNRs of relaxor phase.9–11

Figure 7 shows the temperature dependences of the total

integrated intensities in V-V and V-H spectra. Three charac-

teristic temperatures could be identified from corresponding

anomalies found in both the geometries, TB� 650 K,

T*� 525 K, and TC� 473 K. It may be pointed out that these

characteristic temperatures identified from the Raman data

are in agreement with those found in our recent Brillouin

scattering studies37 on the same sample. On approaching

from high temperature relaxor phase towards the TC, one can

see from Fig. 7(a) that the V-V total integrated intensity

shows a change of slope at TB and T*. Similarly, a change in

slope at TB and TC is found in the plot of total integrated in-

tensity in V-H configuration (Fig. 7(b)).

In the previous studies on Pb-based relaxors, it has been

reported that the Raman modes at 50 and 273 cm�1 are sensi-

tive to the structural transition.10,35 Therefore, it is instructive

to analyze the temperature dependence of these Raman

modes. Since the mode associated with Pb translation10 at

�50 cm�1 is not covered in our spectral range, we restricted

our analysis to the 273 cm�1 mode. This mode is the B-cation-

localized F1u mode of the prototype Fm�3m structure and is

infrared active, whose appearance as a Raman mode arises

from the off-center displacement of B-cations from their ideal

cubic positions.10,33,35 At ambient temperature tetragonal

phase, this mode is A1(TO). Figure 8 shows the behaviour of

FWHM of this mode with temperature. A change of slope at

the intermediate temperature T*� 525 K and a dramatic dis-

continuous change at TC is unambiguously evident. The tran-

sition temperature suggested from the anomalies in Fig. 8 is in

good agreement with that obtained from the temperature de-

pendence of the mode frequencies and the total integrated in-

tensity (Figs. 6 and 7). It may be stressed here that in several

Pb-based relaxors this mode shows a decrease in its width at

T*.10,33,35 Therefore, T* represents an universal character of

the PNRs dynamics, where the strong correlation between the

off-centered displacement of B-site cations begins, leading to

FIG. 7. Temperature dependences of the

total integrated Raman intensity in (a)

V-V and (b) V-H geometry.

FIG. 8. Temperature dependence of FWHM of the mode at 273 cm�1 in

V-V geometry.

073521-6 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15

permanent PNRs.10 A remark on observing different phase

transition temperatures from different techniques is in order.

The difference in the length scale of sensitivity of XRD

(�100 A), dielectric (size of the sample), and light scattering

(�30–40 A) could be the reason for observing different transi-

tion temperatures in different techniques. It may be pointed

out that the length scale of sensitivity depends on the nature of

the interaction between the probing radiation and the sam-

ple.12 Figure 9 shows the temperature dependence of the

depolarization ratio (g). Note that above TB the spectra are

strongly polarized (low g) and depolarization rapidly increases

as T is lowered. This suggests that the correlations among

PNRs increase with decreasing temperature. The depolariza-

tion ratio is found to increase by a factor of �5 as compared

to that obtained at higher temperature. The increase in g is

similar to that reported in other Perovskite relaxor

compounds.10

IV. SUMMARY AND CONCLUSIONS

Dielectric and polarized Raman spectroscopic studies

were carried out on 0.85PZN-0.15PT single crystal in the

temperature range 298 to 873 K. From the dielectric analysis,

the transition is found to be of second order. The polarized

Raman spectra in the ambient temperature tetragonal phase

are assigned for the first time. While in the high temperature

cubic phase (Pm�3m) no first order Raman spectrum is

expected, the presence of several Raman peaks at elevated

temperature suggests substitutional disorder causing the

appearance of symmetry-forbidden Raman bands. Anomalies

in the temperature dependence of line-width of 273 cm�1 F1u

mode (A1(TO) mode at ambient) were found at TC and T*.

Three characteristic temperatures related to the nucleation of

PNRs (TB), formation of long-lived PNRs (T*), and the freez-

ing of their fluctuation (TC) are found to be 650, 525, and

473 K, respectively, from the analysis of Raman spectral

parameters.

ACKNOWLEDGMENTS

We acknowledge Ms. S. Hussain of UGC-DAE-CSR,

Kalpakkam Node for energy dispersive x-ray analysis of the

sample. We also thank Dr. C. S. Sundar for interest in the

work and Director IGCAR for encouragement.

1L. E. Cross, Ferroelectrics 76, 241 (1987).2Z.-G. Ye, Key Eng. Mater. 155–156, 81 (1998).3S.-E. Park and T. R. Shrout, J. Appl. Phys. 82, 1804 (1997).4H. Fu and R. E. Cohen, Nature (London) 403, 281 (2000).5S. Vakhrushev, S. Zhukov, G. Fetisov, and V. Chernyshov, J. Phys.: Con-

dens. Matter 6, 4021 (1994).6I.-W. Chen, P. Li, and Y. Wang, J. Phys. Chem. Solids 57, 1525 (1996).7I.-W. Chen, J. Phys. Chem. Solids 61, 197 (2000).8P. K. Davies and M. A. Akbas, J. Phys. Chem. Solids 61, 159 (2000).9O. Svitelskiy, D. La-Orauttapong, J. Toulouse, W. Chen, and Z.-G. Ye,

Phys. Rev. B 72, 172106 (2005).10N. Waeselmann, B. Mihailova, B. J. Maier, C. Paulmann, M. Gospodinov,

V. Marinova, and U. Bismayer, Phys. Rev. B 83, 214104 (2011).11J. Toulouse, F. Jiang, O. Svitelskiy, W. Chen, and Z.-G. Ye, Phys. Rev. B

72, 184106 (2005).12B. Maier, B. Mihailova, C. Paulmann, J. Ihringer, M. Gospodinov, R.

Stosch, B. G€uttler, and U. Bismayer, Phys. Rev. B 79, 224108 (2009).13W. S. Chang, L. C. Lim, F.-T. Wang, C.-M. Hsieh, and C.-S. Tu, J. Phys.:

Condens. Matter 20, 395229 (2008).14D. La-Orauttapong, J. Toulouse, J. L. Robertson, and Z. G. Ye, Phys. Rev.

B 64, 212101 (2001).15I. K. Jeong and J. K. Lee, Appl. Phys. Lett. 88, 262905 (2006).16D. La-Orauttapong, B. Noheda, Z.-G. Ye, P. M. Gehring, J. Toulouse, D.

E. Cox, and G. Shirane, Phys. Rev. B 65, 144101 (2002).17K. K. Mishra, V. Sivasubramanian, R. M. Sarguna, T. R. Ravindran, and

A. K. Arora, J. Solid State Chem. 184, 2381 (2011).18K. K. Mishra, V. Sivasubramanian, and A. K. Arora, J. Raman Spectrosc.

42, 517 (2011).19K. K. Mishra, A. T. Satya, A. Bharathi, V. Sivasubramanian, V. R. K.

Murthy, and A. K. Arora, J. Appl. Phys. 110, 123529 (2011).20N. K. Karan, R. S. Katiyar, T. Maiti, R. Guo, and A. S. Bhalla, J. Raman

Spectrosc. 40, 370 (2009).21P. S. Dobal, A. Dixit, and R. S. Katiyar, J. Appl. Phys. 89, 8085 (2001).22M. Shen, G. G. Siu, Z. K. Xu, and W. Cao, Appl. Phys. Lett. 86, 252903

(2005).23J. Y. Sun, Y. L. Yang, K. Zhu, Y. Liu, G. G. Siu, and Z. K. Xu, Chin.

Phys. Lett. 25, 290 (2008).24Y. Liu, Y. Jiang, J. Liu, Y. Mo, S. Xie, Z. Zhang, and S. Quan, Phys. Rev.

B 49, 5058 (1994).25J. Cheng, Y. Yang, Y.-H. Tong, S.-B. Lu, J.-Y. Sun, K. Zhu, Y.-L. Liu, G.

G. Siu, and Z. K. Xu, J. Appl. Phys. 105, 053519 (2009).26M. Iwata, Y. Hasegawa, R. Aoyagi, M. Maeda, N. Wakiya, H. Suzuki, and

Y. Ishibashi, Ferroelectrics 378, 84 (2009).27M. EI Marssi and H. Dammak, Solid State Commun. 142, 487 (2007).28F. Jona and G. Shirane, Ferroeletric Crystals (Dover, New York, 1993).29M. Tyunina, M. Plekh, M. Antonova, and A. Klavane, Phys. Rev. B 84,

224105 (2011).30K. Dutta, P. A. Thomas, and K. Roleder, Phys. Rev. B 82, 224105 (2010).31O. Svitelskiy, J. Toulouse, and G. Yong, Phys. Rev. B 68, 104107 (2003).32R. Martinez, R. Palai, H. Huhtinen, J. Liu, J. F. Scott, and R. S. Katiyar,

Phys. Rev. B 82, 134104 (2010).33B. Mihailova, U. Bismayer, B. G€uttler, M. Gospodinov, and L. Konstanti-

nov, J. Phys.: Condens. Matter 14, 1091 (2002).34H. Taniguchi, M. Itho, and D. Fu, J. Raman Spectrosc. 42, 706 (2011).35A.-M. Welsch, B. J. Maier, B. Mihailova, R. J. Angel, J. Zhao, C. Paul-

mann, J. M. Engel, M. Gospodinov, V. Marinova, and U. Bismayer,

Z. Kristallogr. 226, 126 (2011).36M. I. Aroyo, A. Kirov, C. Capillas, J. M. Perez-Mato, and H. Wondrat-

schek, Acta Crystallogr., Sect. A: Found. Crystallogr. 62, 115 (2006).37K. K. Mishra, V. Sivasubramanian, A. K. Arora, and D. Pradhan, e-print

arXiv:1206.7084.38See supplementary material at http://dx.doi.org/10.1063/1.4757958 for

Powder X-ray diffraction pattern of 0.85PZN-0.15PT. Inset:EDAX spec-

trum on single crystal.

FIG. 9. Temperature dependence of the depolarization ratio g¼ IYZ/

(IYZþ IYY) of modes between 700 and 900 cm�1, where IYZ and IYY are the

integrated intensities of corresponding modes in V-H and V-V geometry.

The curve represents a guide to the eye.

073521-7 Mishra et al. J. Appl. Phys. 112, 073521 (2012)

[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:

128.138.73.68 On: Sun, 21 Dec 2014 01:31:15