Phase transformation, improved ferroelectric and magnetic properties of (1x)BiFeO3–xPb(Zr0.52Ti0.48)O3 solid solutionsSubhash Sharma, Vikash Singh, R. K. Dwivedi, Rajeev Ranjan, Avneesh Anshul, S. S. Amritphale, and Navin

Chandra

Citation: Journal of Applied Physics 115, 224106 (2014); doi: 10.1063/1.4882067 View online: http://dx.doi.org/10.1063/1.4882067 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/115/22?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Temperature-independent ferroelectric property and characterization of high-T C 0.2Bi(Mg1/2Ti1/2)O3-0.8PbTiO3 thin films Appl. Phys. Lett. 103, 082902 (2013); 10.1063/1.4819205 Dielectric and structural characterization of high-temperature ferroelectric xBi(Zn1/2Ti1/2)O3yPbZrO3–zPbTiO3perovskite ternary solid solution J. Appl. Phys. 109, 074102 (2011); 10.1063/1.3553874 Enhanced fatigue-endurance of ferroelectric Pb 1 x Sr x ( Zr 0.52 Ti 0.48 ) O 3 thin films prepared by sol-gelmethod Appl. Phys. Lett. 88, 122902 (2006); 10.1063/1.2188591 Fabrication of PbLa 0.05 TiO 3 Pb 1.20 ( Zr 0.52 Ti 0.48 ) O 3 PbLa 0.05 TiO 3 ferroelectric structure onplatinum electrodes by a sol-gel process Appl. Phys. Lett. 87, 252907 (2005); 10.1063/1.2150275 Dielectric and ferroelectric response as a function of annealing temperature and film thickness of sol-geldeposited Pb(Zr 0.52 Ti 0.48 )O 3 thin film J. Appl. Phys. 86, 2700 (1999); 10.1063/1.371114

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Phase transformation, improved ferroelectric and magnetic propertiesof (1 2 x) BiFeO3–xPb(Zr0.52Ti0.48)O3 solid solutions

Subhash Sharma,1,a) Vikash Singh,1 R. K. Dwivedi,1,a) Rajeev Ranjan,2 Avneesh Anshul,3

S. S. Amritphale,3 and Navin Chandra3

1Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology,A-10, Sector-62, Noida-201307, Uttar Pradesh, India2Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India3Advanced Materials and Processes Research Institute, CSIR, Bhopal 462026, India

(Received 10 March 2014; accepted 27 May 2014; published online 11 June 2014)

The authors prepared (1� x)BiFeO3 – (x)Pb(Zr0.52Ti0.48)O3 for x� 0.30 by sol-gel method and

investigated the material’s structures, magnetic and electrical properties. Detailed Rietveld analysis

of X-ray diffraction data revealed that the system retains distorted rhombohedral R3c structure for

x� 0.10 but transforms to monoclinic (Cc) structure for x> 0.10. Disappearance of some Raman

modes corresponding to A1 modes and the decrease in the intensities of the remaining A1 modes

with increasing x in the Raman spectra, which is a clear indication of structural modification and

symmetry changes brought about by PZT doping. Enhanced magnetization with PZT doping

content may be attributed to the gradual change and destruction in the spin cycloid structure of

BiFeO3. The leakage current density at 3.5 kV/cm was reduced by approximately three orders of

magnitude by doping PZT (x¼ 0.30), compared with BFO ceramics. VC 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4882067]

INTRODUCTION

Magneto-electric material with exchange interaction due

to reorganization of crystallographic domain and structural

phase transition is interesting due to application in spin based

electronics.1,2 Magnetic moment interaction of magnetic

oxide and coupling with nanostructural interface is of

interest for device applications.3,4 Bismuth Iron Oxide

(BiFeO3) exhibits ferroelectricity (Tc� 1103 K) and

anti-ferromagnetism (TN� 643 K) at room temperature

which makes it the potential candidate in the field of

information technology and optoelectronic devices.5,6

Non-centrosymmetric ferroelectric structure is due to strong

hybridization of Bi (6 p) ions and O (2p), with Bi (6S2) lone

pair electron in BFO perovskite ceramic.7,8 Fe3þ cations (d4)

at B-sites in BFO contribute magnetization. The material to

demand technological applications need certain issues to be

addressed like weak ferromagnetism near room temperature

and high conductance.9 High leakage current in the BFO

samples is due to oxygen vacancies, and valence fluctuation

of Fe ions (Fe2þ and Fe3þ) along with formation of second-

ary phase.10–12

Recently, an enormous deal of experiment has revealed

improvement in understanding of structural and multiferroic

properties in BFO. The solid solution of BiFeO3–ABO3 per-

ovskite materials has been investigated to minimize the high

electric leakage of BiFeO3 materials.13,14 Structural phase

transformation is modified with occurrence of intermediate

phase in BiFeO3.15 The perovskites containing Pb or Bi cati-

ons are of particular importance due to their stereo-chemical

activity which makes them promising materials in the field of

magneto-electrics.16,17 The comprehensive study of solid sol-

utions of BFO–PZT ceramic samples prepared by sol-gel

route has been reported in this paper. The systematic crystal-

lographic study of solid solutions samples with x� 0.30 were

reported along with structural, ferroelectric, dielectric, and

magnetic properties.

EXPERIMENTAL

Polycrystalline samples with x¼ 0.00, 0.10, 0.20, and

0.30 in (1� x)BiFeO3�(x)Pb(Zr0.52Ti0.48)O3, i.e., (1� x)

BFO-(x)PZT system were prepared by sol gel method. The

raw materials of high purity reagents Pb(CH3CO2)23H2O,

Zr(OCH2CH2CH3)4, Ti[OCH(CH3)2]4, Bi(NO3)2.5H2O,

Fe(NO3)2.9H2O were used as the starting materials along

with 2-methoxyethanol (CH3OCH2CH2OH) and acetic acid

as the solvents. The detail of synthesis process is earlier

reported.18 The crystal structure was determined using X ray

diffractometer (Shimadzu XRD-6000) with Cu Ka radiation.

The data were further analyzed via the Rietveld refinement

using FullProf structural analysis software. Raman spectra of

these samples were recorded by Renishaw in Via Reflex

Raman spectrometer. Ferroelectric, dielectric, and magnetic

measurements were carried out using P-E Loop Tracer

(Marine India), Impedance Analyser (Novo Control,

Germany) and SQUID magnetometer, respectively.

STRUCTURAL ANALYSIS

X-ray diffraction patterns for the compositions x� 0.30

in the (1� x)BFO-(x)PZT system are shown in Fig. 1(a).

The XRD pattern of BFO (x¼ 0) confirms the rhombohedral

structure. Traces of visible impurity phases like Bi2Fe4O9

and Bi25Fe2O39 have been found in BFO-PZT (X¼ 0.20 and

x¼ 0.30) samples. These impurity phase formation also

a)Authors to whom correspondence should be addressed. Electronic

addresses: rk.dwivedi@jiit.ac.in and subhash1jiit@gmail.com

0021-8979/2014/115(22)/224106/7/$30.00 VC 2014 AIP Publishing LLC115, 224106-1

JOURNAL OF APPLIED PHYSICS 115, 224106 (2014)

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reported in earlier reports.19,20 It is observed that peak profile

corresponding to 2h� 32� changes with increasing x.

Magnified pattern in the vicinity of 2h� 32� corresponding

to the reflections (104) and (110) are shown Fig. 1(b). For

x¼ 0.0 and 0.10, these reflections are clearly distinguishable,

indicating the rhombohedral structural symmetry. These

reflections appear to merge into one peak along with asym-

metric broadening which shifts towards low angle side with

increasing x. Merging of the two peaks into one may be the

signature of structural transformation and similar type of

structural phase transitions have been reported in BFO with

different dopants.21–23

To confirm this, we further analyze the XRD data with

Rietveld refinement using FullProf software.24 The initial

Rietveld refinement was carried out using zero point shift,

the unit cell and background parameters. The background

was modelled using linear interpolation between a set back-

ground points with refinable heights and peak shapes which

were described by pseudovoigt functions. Fig. 2 shows the

experimental and refined XRD patterns for all these samples.

The fitting between experimental and refined data was found

to be relatively good based on the values of agreement fac-

tors. Refined structural parameters along with profile

R-factors and different bond lengths and bond angles are

listed in Table I. For x¼ 0.0 and 0.10, the diffraction data

were found to fit well with the Rietveld refined data on the

basis of rhombohedral (R3c) structural symmetry. It has

been observed that for x¼ 0.0, Bi-O and Fe-O bond lengths

in a plane (a-b plane) are 2.18 A and 1.82 A, respectively,

and corresponding Bi–O–Bi and Fe-O-Fe angles are 112.71�

and 151.51�, where as for x¼ 0.10, corresponding bond

lengths are 2.21 A, 1.75 A, and bond angles are 110.44� and

154.55�, respectively. It shows that with inclusion of Pb2þ in

place of Bi3þ and (Zr/Ti)4þ in place of Fe3þ for x¼ 0.10,

Bi/Pb-O bond length increases from 2.18 A to 2.21 A and

Fe/Ti–O bond length decreases from 1.818 A to 1.754 A indi-

cating structural distortion for x¼ 0.10, however, crystal

structure remains stable in R3c symmetry.

It can be understood in terms of fitting factors Rwp and

v2, which changes from 7.45 and 2.20, respectively, for

x¼ 0.0 to 4.23 and 1.86 for x¼ 0.10. The fitting parameters

are obtained well within the limit of agreement. Further,

refinement for x¼ 0.20 and 0.30 samples was carried out

with four structural models to analyse crystal structure, i.e.,

R3cþP4mm, R3c þ Pnma, R3c þ Cc and Cc. The refine-

ment of BFO-PZT (x¼ 0.20, 0.30) have good match well

with monoclinic symmetry (Cc). The fitting profile data

shows significant change in Bi-O and Fe-O bond length from

2.180 A and 1.818 A (for x¼ 0) to 2.232 A and 1.690 A (for

x¼ 0.20), and 2.265 A and 1.692 A (for x¼ 0.30). In addi-

tion to this, a remarkable change in Bi-O-Bi and Fe-O-Fe

angles from 110.44� and 154.55� (for x¼ 0.10) to 112.51�

and 164.92� (for x¼ 0.20), and 100.02� and 165.17� (for

x¼ 0.30) is noted. Based upon observed and calculated pat-

terns as well as the values of their agreement factors Rwp

(5.77 for x¼ 0.20 and 4.91 for x¼ 0.30) and v2 (1.94 for

both), monoclinic (Cc) structure for x¼ 0.20 and 0.30 is pro-

posed. It has been observed from Table I that lattice parame-

ters along with crystal structure have got influenced with

increasing x. This is expected as the ions of larger ionic radii

of Pb2þ(1.49 A) and Zr4þ (0.72 A)/Ti4þ (0.68 A) as com-

pared to that Bi3þ (1.30 A) and Fe3þ (0.64 A) in the parent

lattice, which produces lattice distortions, strains and hence

modify lattice size of the solid solution compounds resulting

structural transformation with increasing x.25 The average

crystallite size for all samples has been calculated from XRD

peak broadening using the Debye Scherrer’s formula and

tabulated in Table II.

D ¼ Kkb cos h

; (1)

where D is crystallite size, K (constant)¼ 0.89, b is the full

width at half maxima, and h is the Bragg’s angle.

RAMAN SPECTROSCOPY

Raman spectra of these samples are shown in Fig. 3.

The BFO ceramic sample is characterized by rhombohedral

FIG. 1. (a) XRD patterns for x¼ 0.00, 0.10, 0.20, and 0.30 in the

(1� x)BFO-(x)PZT system. (b) Expanded pattern in the 2h range 30�-33� (*

Bi25Fe2O39 and # Bi2Fe4O9).

FIG. 2. Observed (dotted), calculated (continuous line), and difference (bot-

tom line) profiles obtained after the Rietveld refinement for x¼ 0.00, 0.10,

0.20, and 0.30 in the (1� x)BFO-(x)PZT system.

224106-2 Sharma et al. J. Appl. Phys. 115, 224106 (2014)

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symmetry with the point group R3c (C63v). The Raman

active modes of the structure can be summarized using the

irreducible representation CRaman¼ 4A1þ 9E. BFO sample

shows 11 Raman active modes out of 13 reported modes in

rhombohedral R3c sample.26 BFO-PZT shows even less

Raman modes due to the development of local stress and a

large number of point defects in samples. The point defects

and local stress in the BFO-PZT samples lead to a local low-

ering of symmetry and caused band broadening in Raman

spectra.26 The reported Raman peak positions of BFO from

the literature27–29 and Raman spectra of our samples are

compared in Table II.

Here, we have observed four A1 (A1�1, A1

�2, A1�3, and

A1�4) modes and seven E modes, which are depicted in

Table II. The intensities of a few of A modes are greater than

E modes in the present spectra. Raman measurements

were carried out in an un-polarized configuration. The

stereo-chemical activity of Bi and Pb lone pair of electrons

plays the main role in changing both Bi–O covalent bonds

and six characteristic modes E�1, A1�1, A1

�2, A1�3, A1

�4,

and E�2. These modes are believed to be responsible for the

ferroelectric nature of the bismuth ferrite samples.27 As evi-

dent from XRD analysis, the crystal symmetry varies from

rhombohedral R3c to monoclinic (Cc) on subsequent doping

of PZT in the BFO. This change in crystal structure leads to

the shift of Raman modes at lower frequencies and the change

in the shape of A modes responsible for stereo-chemical activ-

ity. The strong characteristic modes corresponding to Bi–O

covalent bond (A1�1, A1

�2, and A1�3) shift toward a lower

wave number with increasing PZT content compared to pure

BFO. This may be attributed to the lower atomic weight of

Pb2þ (207.2) and Ti4þ (47.867) as compared to Biþ3 (208.98)

TABLE I. Refined structural parameters for x� 0.30 in the (1� x)BFO-(x)PZT system.

Samples Lattice parameters Atoms x y z Bond Lengths Bond Angle R-factors (%)

x¼ 0.0 a¼ 5.5757 (A) Bi/Pb 0.0 0.0 0.0 Bi-O3 2.180 Fe-O-Fe 151.505 Rwp¼ 7.45

c¼ 13.8630 (A) Fe/Zr/Ti 0.0 0.0 0.2800 2.572 Bi-O-Fe 95.595 Rp¼ 5.66

R3c V¼ 373.2396 (A3) O 0.8716 0.6293 0.4968 Fe-O3 1.818 Bi-O-Bi 112.707 RF¼ 3.91

2.698 RB¼ 3.86;v2¼ 2.20

x¼ 0.10 a¼ 5.5882 (A) Bi/Pb 0.0 0.0 0.0 Bi-O3 2.201 Fe-O-Fe 154.546 Rwp¼ 4.23

c¼ 13.8648 (A) Fe/Zr/Ti 0.0 0.0 0.2757 2.621 Bi-O-Fe 96.837 Rp¼ 3.26

R3c V¼ 374.9619 (A3) O 0.8705 0.6423 0.4943 Fe-O3 1.754 Bi-O-Bi 110.442 RF¼ 3.85

2.701 RB¼ 3.97;v2¼ 1.86

x¼ 20 a¼ 9.7173 (A) Bi/Pb 0.0 0.2500 0.0 Bi-O3 2.232 Fe-O-Fe 164.923 Rwp¼ 5.77

b¼ 5.5620 (A)

c¼ 5.6277 (A);

b¼ 125.822

Fe/Zr/Ti 0.2471 0.2447 0.6968 2.700 Bi-O-Fe 100.039 Rp¼ 4.38

Cc V¼ 246.6310 (A3) OI �0.0160 0.2767 0.5885 Fe-O3 1.690 Bi-O-Bi 112.507 RF¼ 1.93

OII 0.3370 0.4490 0.0600 RB¼ 2.57;v2¼ 1.94

OIII 0.3010 0.0400 �0.0400 2.318

x¼ 0.30 a¼ 9.7206(A) Bi/Pb 0.0 0.2500 0.0 Bi-O3 2.265 Fe-O-Fe 165.170 Rwp¼ 4.91

b¼ 5.5674(A)

c¼ 5.6245(A)

b¼ 125.786

Fe/Zr/Ti 0.2471 0.2497 0.70131 Fe-O3 2.734 Bi-O-Fe 95.629 Rp¼ 3.34

Cc V¼ 246.9238 (A3) OI �0.0019 0.2767 0.5885 Fe-O3 1.692 Bi-O-Bi 100.018 RF¼ 1.93

OII 0.3370 0.4490 0.0600 RB¼ 2.57;v2¼ 1.94

OIII 0.3010 0.0400 �0.0400 2.354

TABLE II. Comparison of Raman mode positions (cm-1) from the present study and the literature.

Raman modes Yuan et al.29 Singh et al.28 Fukumura et al.27 BFO BP10 BP 20 BP30

A1�1 126 136 147 139 135 130 132

A1�2 165 168 176 172 166 155 …

A1�3 213 211 227 210 209 212

A1�4 425 425 490 490 469 477 477

E�1 111.7 77 … 264 258 260

E�2 259.5 275 265 280 273 278

E�3 … 335 279 331 306

E�4 339.6 365 351 366 343

E�5 366.9 … 375 432 430

E�6 473.3 456 437 522 518 513 523

E�7 599 597 525 556 529

224106-3 Sharma et al. J. Appl. Phys. 115, 224106 (2014)

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and Fe3þ (55.845). Since the wave number of the Raman

modes are dependent on force constant and ionic mass.

However, the modes E�1, E�3, E�4, and E�5 are suppressed

completely for x¼ 0.20 sample and A1�2, A1

�3 and some E

modes are also completely absent for x¼ 0.30. Moreover,

A1�2 mode’s intensity has been found to decrease drastically

from x¼ 0.0 to x¼ 0.30 samples, which may be due to the

structural distortion from rhombohedral to monoclinic (Cc)

structure. The disappearance of some peaks corresponding to

A1 modes and a decrease in intensities of the remaining A1

modes confirms the transformation of crystal structure with

doping.30 The Raman spectra of doped samples are quite dif-

ferent from that of the BFO in space group Pnma31 and

Pn21a.32 Thus, Raman studies reveal substitution-induced

structural phase transition from rhombohedral to monoclinic

(Cc) with increasing x.

MAGNETIC PROPERTIES

The magnetic properties of pure BFO and PZT substi-

tuted BFO samples were carried out at room temperature

with a maximum field of 20 kG. Fig. 4 shows the measure-

ment of the M-H hysteresis loops for all the samples. Weak

magnetic hysteresis behavior was observed for pure BFO

with a magnetization value of 0.0062 emu/g, due to exis-

tence of canted antiferromagnetic spins induced by size

effect. As generally reported,33 bulk BFO exhibits antifer-

romagnetism without any saturation magnetization. Weak

ferromagnetism in pure BFO always ascribed to the size

effects (45 nm for pure BFO in present case) of the suppres-

sion of helical order.34–36 The substitution of 10% PZT in

BFO enhances the magnetization in the sample to

0.0723 emu/g. This enhancement of the magnetic behavior

with x substitution can be attributed to structural distortion

due to insertion of (Ti/Zr)4þ in place of Fe3þ, leading to the

collapse and suppression of the space modulated cycloid

spin structure, a property exhibited by other dopants.34–37

Distortion in structure results in the canting of spins and

hence the bond angle (Fe-O-Fe) changes from 151.51� to

165.17�. Consequently, an increase in the canting angle

modifies the magnetic properties, as reported in related

FIG. 4. M-H hysteresis loops for

x� 0.30 in the (1� x)BFO-(x)PZT

system.

FIG. 3. (a) Raman spectra for various

compositions x� 0.30 in (1� x)BFO -

(x)PZT system. (b) Gaussian fitted pro-

file of Raman spectra for x¼ 0.0.

224106-4 Sharma et al. J. Appl. Phys. 115, 224106 (2014)

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literature.38 The Mr value significantly increases for

x¼ 0.20 and 0.30 (Table III and Fig. 4). The PZT doping

below 0.10, the spin cycloid structure get suppressed result-

ing marginal increase in magnetization. The phase transfor-

mation from rhombohedral symmetry in BFO to

monoclinic symmetry (Cc) at x¼ 0.20 and 0.30 leading to

collapse of the cycloidal spin structure and field induced

spin reorientation, resulting significant increase in magnet-

ization.37 Magnetization in the sample due to impurity

phases Bi2Fe4O9 and Bi25Fe2O39 has marginal effect as

these are reported as non magnetic.38

ELECTRICAL BEHAVIOUR

Fig. 5 shows the curves of the leakage current density (J)

as a function of the applied electric field (E). The BFO sample

has a higher leakage current density and consequently it was

easily broken under a higher applied electric field. At an

applied electric field of 3.5 kV cm�1, the leakage current den-

sities of these samples were 0.014 A cm�2, 0.00415 A cm�2,

2.18� 10�4 A cm�2, and 3.75� 10�5 A cm�2 for x¼ 0.0,

0.10, 0.20, and 0.30, respectively. It has been observed that

leakage current density shows a linear decrease in J with the

increase in x (Fig. 5). The decrease in J with increasing x

values might be explained as the reduction in charge defects

(oxygen vacancies or bismuth vacancies, etc) resulting from

the increasing doping of high valence (Zr/Ti)4þ ions.39 As we

all know, the high leakage current densities in pure or doped

BFO ceramics originated mainly from charge defects such as

bismuth vacancies V3þBi and oxygen vacancies V2þ

O , which

came mainly from Bi volatility and the transition from Fe3þ to

Fe2þ.40

The room temperature ferroelectric hysteresis (P-E)

loops for x� 0.30 at 50 Hz are shown in Fig. 6. Remnant

polarization Pr � 2.05 lC/cm2 has been observed in BFO

TABLE III. Magnetic and electrical polarisation parameters for x� 0.30 in the (1� x)BFO - (x)PZT system.

Sample Size (nm) Ms at RT (emu/g) Hc (G) Mr (emu/g) Ec (kV/cm) Pr (lC/cm2)

x¼ 0.0 45 … 845 0.0068 4.8230 2.0556

x¼ 0.10 35 0.1198 4128 0.0768 6.8846 4.3675

x¼ 0.20 27 0.6256 2491 0.3777 8.4906 6.0623

x¼ 0.30 25 0.8333 2567 0.4596 6.6307 6.4637

FIG. 6. P-E hysteresis loops measured

at 50 Hz for x� 0.30 in the

(1� x)BFO - (x)PZT system.

FIG. 5. Leakage current as a function of applied electrical field in (1� x)

BFO-(x)PZT ceramics with x� 0.30.

224106-5 Sharma et al. J. Appl. Phys. 115, 224106 (2014)

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sample under an applied field of �20 kV/cm, which is con-

sistent and even better with the earlier reports on bulk

BFO.41–43 P-E loop shows high dielectric loss or leakage

current in BFO sample, which is in accordance with leakage

current measurement. All doped samples have exhibited

improved polarisation. Pr has been found to be increased

from 2.05 lC/cm2 for x¼ 0.0 to Pr¼ 6.46 lC/cm2 for

x¼ 0.30. Improvement in the hysteresis loop with the higher

concentration of x, i.e., PZT could be explained as first, it

confirms stable ferroelectric domain in the system.44 Second,

BFO possesses relatively large leakage current than

BFO-PZT (x¼ 0.30) that restrict reversal of polarisation

which is further confirmed by leakage current measurement

for all samples (Fig. 6). Third, introducing Pb ions into the

Bi is expected to restrict Bi evaporation and hence control

the formation of O-vacancies which is due to high bond

energy of Pb-O bond (3.9 eV) as compared to Bi- O bond

(1.7 eV).45 PZT, being good insulating materials, increases

the sample resistivity (confirmed by leakage current mea-

surement). Meanwhile, PZT doping may form defect dipoles

which restrict domain wall motion.44

Figs. 7(a) and 7(b) illustrate the dependence of dielectric

constant (er) and loss tangent (tan d) on frequency for all

samples at room temperature. The dielectric constant (er)

decreases with increasing frequency in all the samples and

shows two plateaus, one in intermediate frequency range and

other in higher frequency range. These two plateaus are

clearly distinguished for x� 0.10 and less distinguished for

x¼ 0.20 and 0.30 in BFO-PZT samples. Dielectric loss

(tan d) has shown dispersion in low frequency range and dis-

persion frequency has been found to decrease with increas-

ing x. The dependence of er and tan d in the entire frequency

range can be explained on the response of defects complexes

with applied filed. The large value of er at lower frequency is

due to the combined response of all type of polarisations

(such as space charge, orientation etc.). The formation of

charge defects due to volatilization of bismuth during sinter-

ing may lead to the creation of bismuth and oxygen vacan-

cies as per the following reaction:

Bi2O3 () 2Bi3þ þ 3 O2� ! 2V000Bi þ 3V••O þ Bi2O3; (2)

V••O þ e� () V•

O: (3)

In the above equations, negatively charged bismuth vacan-

cies (V00Bi) are compensated by positively charged oxygen

vacancies (V••O) in order to maintained charge neutrality in

these materials.46 Low value of er in high frequency region

indicates that dipoles with small effective masses (e.g., elec-

trons) mainly contribute to dielectric constant instead of

charge defects with large effective masses (e.g., oxygen

vacancies) whose effect is observed in low frequency region

as a result of space charge formation at the grain boundaries.

Such behaviour can be well described by the Maxwell-

Wagner model,47 which is related to the space charge relaxa-

tion at the interfaces of grain and grain boundaries. These

space charge carriers originate from oxygen (V••O) and bis-

muth (V000Bi) vacancies and can follow the applied electric field

at low frequencies and contribute to the dielectric constant.

At higher frequencies, the defect dipoles like (VBi�VO)0

may not have time to follow the applied field and undergo

relaxation as we can see in these plots.

CONCLUSION

In summary, solid solutions of (1� x)BiFeO3 – xPb

(Zr0.48Ti0.52)O3 (0.00 � x � 0.30) polycrystalline sample

were synthesized by sol-gel route. Rietveld refinement

results of X-ray diffraction spectra show a compositional

driven structural phase transition from rhombohedral (R3c)

symmetry for x¼ 0.0 and 0.10 to monoclinic (Cc) symmetry

for x¼ 0.20 and 0.30, which is confirmed by change in peak

profile of the vibrational modes in Raman spectra. Remnant

magnetization has been found to increase with x, which may

be attributed to destruction of spin cycloid structure due to

insertion of Zr/Ti in Fe-O-Fe network of BFO lattice and

phase transition. The enhanced ferroelectric polarization

with increasing x is caused by reduction in leakage current

for x¼ 0.30.

ACKNOWLEDGMENTS

We thankfully acknowledge the financial support from

DST, Government of India for this work via Project (No.

SR/S3/ME/0048/2009-SERC) and NRC-M, IISc Bangalore.

One of the authors, Mr. Subhash Sharma is also thankful to

Jaypee Institute of Information Technology, Noida for

Teaching Assistantship.

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