Materials Chemistry and Physics 121 (2010) 147–153
Contents lists available at ScienceDirect
Materials Chemistry and Physics
journal homepage: www.elsevier.com/locate/matchemphys
Structural and dielectric relaxor properties of yttrium-doped
Ba(Zr0.25 Ti0.75 )O3 ceramics
T. Badapanda a,∗ , S.K. Rout b,∗∗ , L.S. Cavalcante c , J.C. Sczancoski c , S. Panigrahi a , T.P. Sinha d , E. Longo c
a
Department of Physics, NIT, Rourkela 769008, India
Department of Applied Physics, BIT, Mesra, Ranchi, India
LIEC, Universidade Estadual, Paulista, P.O. Box 355, 14801-907, Araraquara, SP, Brazil
d
Department of Physics, Bose Institute, 93/1 A.P.C. Road, Kolkata 700009, India
b
c
a r t i c l e
i n f o
Article history:
Received 2 February 2009
Received in revised form
11 September 2009
Accepted 3 January 2010
Keywords:
Ceramics
Sintering
Microscopy
Electrical properties
a b s t r a c t
In this work, [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics with different concentrations (x = 0, 0.01, 0.025 and
0.05) were synthesized by Solid state reaction. The X-ray diffraction patterns indicated that these crystalline ceramics have a perovskite-type cubic structure. The scanning electron microscopy micrographs
revealed that the addition of yttrium (Y) into the lattice is able to change the microstructure. The temperature dependent dielectric properties were investigated in the frequency range from 1 kHz to 1 MHz.
The relaxor property was analyzed by the broadening of the maximum dielectric permittivity as well as
its shifting to high temperatures with the variation of frequency measurements. The Curie temperature
decreases with the addition of Y content into the lattice. The diffusivity and the relaxation strength were
estimated using the modified Curie–Weiss law. The relaxation time of these materials was well-adjusted
by the Vogel–Fulcher equation.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
The ferroelectric materials are divided into two different classes:
classical or relaxor ferroelectrics [1]. In particular, relaxor ferroelectrics have been widely investigated because of its interesting
electrical properties, which can be employed in different technological applications [2,3]. The main characteristic of this material
group is the extraordinary large, diffuse and frequency dispersive maximum in the temperature (Tm ) dependence of dielectric
permittivity (εm ). This typical phenomenon is caused by the
presence of polar nano-regions (PNR) into the structure. The
ferroelectric–relaxor behavior of ceramic materials is characterized by a diffuse phase transition, which has been investigated
theoretically as well as experimentally results in literature [4–15].
In the last years, several physical models have been proposed
in order to explain the relaxor properties, mainly including: microscopic mechanism of polarization [16], order–disorder transition
[17], microdomain and macrodomain switching [18], dipolar-glass
model [19], and quenched random field model [20]. In spite of
these fundamental studies, the origin of the relaxor properties
is not completely understood yet. Currently, it is well-accepted
that the relaxor nature can be arising from micropolar regions
∗ Corresponding author. Tel.: +91 9437306100 (India).
E-mail addresses: badapanda.tanmaya@gmail.com (T. Badapanda),
skrout@bitmesra.ac.in (S.K. Rout).
0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.matchemphys.2010.01.008
into the lattice, as consequence of the B-site substitution by
ions with different atomic radii and/or chemical valences [21].
Generally, the relaxor ferroelectrics belong to the disordered
material families with perovskite structure and general chemi
cal formula A1−x Ax B1−y By O3 [22]. In principle, the most studied
relaxors are Pb(Mg1/3 Nb2/3 )O3 (PMN), Pb(Sc1/2 Ta1/2 )O3 (PST) and
Pb1−x Lax (Zr1−y Tiy )O3 (PLZT) [23–28]. The main drawback of these
materials is related to the presence of PbO in its compositions,
which is a toxic compound with high volatility [29]. Thus, the preoccupation with the environment has directed the researches toward
to the synthesis of Pb-free oxides. Based on this purpose, several
relaxor compounds with perovskite-type structure were prepared
and characterized in the last years [30–34].
In solid state systems, the barium zirconate titanate
Ba(Zrx Ti1−x )O3 is an attractive ceramic due to its structural
and physical properties depend on titanium (Ti) and zirconium
(Zr) contents into the matrix [35,36]. The Ba(Zrx Ti1−x )O3 phase
has a rhombohedral structure when the Zr content is added up to
x = 0.05 into the lattice [37]. For compositions with Zr. Content
up to x > 0.08, shows orthorhombic structure at room temperature [37] and exhibits a broad dielectric constant temperature
(ε∼T ) curve near the Tm . This phenomenon has been explained
by the existence of an inhomogeneous distribution of Zr4+ ions
into the Ti sites and/or by the mechanical stresses on the grains
[38]. The increase of Zr content x∼0.20 into the Ba(Zrx Ti1−x )O3
matrix induces a phase transition from tetragonal to pseudo cubic
structure as well as a limit between ferroelectric/relaxor behavior
148
T. Badapanda et al. / Materials Chemistry and Physics 121 (2010) 147–153
[39]. Ravez and Simon [40] observed a relaxor-like behavior in
Ba(Zrx Ti1−x )O3 ceramics with Zr content up to x ≥ 0.25. On the
other hand, Tang et al. [41] reported that high Zr contents (x = 0.30
and 0.35) result in “slim” hysteresis loops, which is a typical
relaxor–ferroelectric characteristic. Normally, it is attributed to
the distribution of micropolar regions along the structure [42].
Karan et al. [43] reported on the relaxor properties and raman
spectral studies of Ba(Zrx Ti1−x )O3 ceramics using different concentrations (0.5 ≤ x ≤ 1.0) at several temperatures. Therefore, in this
work, we report on the structural and dielectric relaxor behavior
of yttrium (Y) doped of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics with
different concentrations (x = 0, 0.01, 0.025 and 0.05) synthesized
by solid state reaction.
2. Experimental
2.1. Synthesis and characterization of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics
The [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics were prepared by solid state reaction
route (SSR). In this synthesis method, barium carbonate (BaCO3 ) (S.D. Fine Chem.,
Mumbai), titanium oxide (TiO2 ) (E. Merck India Ltd.), zirconium oxide (ZrO2 ) (Loba
Chem., Mumbai) and yttrium oxide (Y2 O3 ) (E. Merck India Ltd.) were used as raw
materials. All these chemical compounds have more than 99% purity. In the initial
synthesis stage, these compounds were stoichiometrically mixed using isopropyl
alcohol (IPA) and milled with an agate mortar up to obtain the homogenous powders.
Afterwards, these powders were heat treated at 1623 K for 4 h in a programmable
furnace.
The synthesized powders were characterized by X-ray diffraction (XRD) using
a DMax/2500PC diffractometer (Rigaku, Japan). XRD patterns were obtained using
Cu K˛ radiation in the 2 range from 5◦ to 75◦ with a scanning rate of 0.02◦ /s. The
average grain size was estimated with a JSM T330 scanning electron microscopy
(SEM) (Jeol, USA) operated at 25 keV. In order to measure the electrical properties,
the [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics with different compositions were uniaxially
pressed into disk shapes using a pressure of 200 MPa. A polyvinyl alcohol (PVA)
solution (2 wt%) was employed as binder for these ceramics during this experimental
process. In the sequence, these disks were then sintered at 1673 K for 4 h in air
atmosphere and its densities were evaluated using the Archimedes’ principle. The
silver electrodes were printed on the opposite disk faces followed by heat treatment
performed at 973 K for 15 min. The dielectric measurements were carried out in the
frequency range from 1 kHz to 1 MHz using a LCR tester (Hioki, Japan) connected
to computer. The dielectric data were collected every 3 K, keeping a heating rate of
0.5 K/min.
3. Results and discussion
Fig. 1 shows the XRD patterns of [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3
ceramics
prepared
with
different
concentrations
x=
0, 0.01, 0.025, 0.05.
The XRD patterns showed that all ceramics have a perovskitetype cubic structure with space group Pm3̄m, in agreement
with the respective Joint Committee on Powder Diffraction Standards (JCPDS) card no . 36-0019 [44]. In addition, diffraction
peaks corresponding to the secondary phases (Y2 O3 ) were not
detected, indicating that the Y3+ ions were incorporated into the
Ba(Zr0.25 Ti0.75 )O3 matrix.
It has been reported in the literature that the XRD patterns can
be employed as structural characterization tool in order to evaluate the crystallinity or degree of order–disorder at long-range of
the materials [45]. Considering this supposition, the intense and
well-defined diffraction peaks observed in Fig. 1 suggest that these
ceramics are structurally ordered at long-range.
Fig. 2 shows the lattice parameter as well as the unit cell volume
results of [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics. These data were
estimated through the UNITCELL-97 program [46] using the regression diagnostics combined with nonlinear least squares.
As it can be seen in this figure, the results indicated that the addition of Y3+ ions into the Ba(Zr0.25 Ti0.75 )O3 phase slightly reduced
the lattice dimensions. Recently, Shan et al. [47] explained that the
substitution of Ba atoms by those of Y is able to induce distortions
into the Ba(Zr0.25 Ti0.75 )O3 phase because of the differences between
Fig. 1. XRD patterns of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics prepared with different
concentrations [(a) x = 0, (b) 0.01, (c) 0.025 and (d) 0.05] and sintered at 1673 K for
4 h.
the atomic radii. According to literature [47,48], the ionic radius of
Ba2+ ions is 0.161 nm, while that of Y3+ is 0.086 nm. On the basis of
these assumptions, it is possible to conclude that the substitution
of B-sites commonly occupied by Ba2+ ions by those of Y3+ tends
to promote an electronic compensation into the matrix. It can be
described by the following Kröger–Vink equation:
Y2 O3
Ba(Zr0.25 Ti0.75 )
−→
2Y•Ba + VBa + 3OxO
(1)
This equation implies that for every two Y3+ ions positioned on the
A-site, one cationic vacancy VBa is necessary to promote the charge
neutrality. In this case, the concentration of vacancies is higher,
when there is an increase of Y content into the lattice.
Fig. 3 shows the schematic representation of crystalline (a) pure
and (b) Y-doped Ba(Zr0.25 Ti0.75 )O3 supercells (1 × 2 × 2).
In both supercells, the Ti and Zr atoms (lattice formers) are
bonded to six oxygens in an octahedral configuration, i.e., forming
the [TiO6 ] and [ZrO6 ] clusters (Fig. 3(a and b)). In the non-polar
[ZrO6 ] clusters, the Zr atoms occupy a centrosymmetric position into the octahedral, while in the polar [TiO6 ] clusters, the
Ti atoms are slightly displaced along the [0 0 1] direction [49].
This displacement or distortion is supposed to be caused by the
covalent character between the O–Ti–O bonds (directional orientations) into the perovskite-type structure [50,51]. On the other
Fig.
2. The
lattice
parameter
values
and
unit
cell
volume
[Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics as a function of Y content into the lattice.
of
T. Badapanda et al. / Materials Chemistry and Physics 121 (2010) 147–153
149
Fig. 3. Schematic representation of (a) pure and (b) Y-doped Ba(Zr0.25 Ti0.75 )O3 supercells, illustrating the [TiO6 ], [ZrO6 ] and [BaO12 ] clusters.
hand, the Ba atoms (lattice modifiers) are bonded to twelve oxygens, resulting in a dodecahedron-type geometry known as [BaO12 ]
clusters (ionic bond with radial orientation) (Fig. 3(b)). Therefore,
the structural order–disorder as well as the polarization mechanisms into the cubic Ba(Zr0.25 Ti0.75 )O3 phase are caused by the
existence of polar [TiO6 ] clusters close to those of [BaO12 ]. In the
crystalline Y-doped Ba(Zr0.25 Ti0.75 )O3 supercell, the Y atoms are
able to substitute the sites occupied by Ba atoms, resulting in
the formation of [YO6 ] clusters [52]. In principle, future investigations will be performed by means of X-ray absorption near-edge
structure and extended X-ray absorption fine structure spectroscopies to understand the influence of Y3+ ions on the number
coordination and local non-centrosymmetry of Ba(Zr0.25 Ti0.75 )O3
ceramics.
Fig. 4. SEM micrographs of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics prepared with different concentrations (a) x = 0, (b) 0.01, (c) 0.025 and (d) 0.05.
150
T. Badapanda et al. / Materials Chemistry and Physics 121 (2010) 147–153
Fig. 5. Temperature dependence of real and imaginary dielectric permittivity performed at different frequencies for the [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics prepared with
different concentrations: (a) x = 0, (b) 0.01, (c) 0.025 and (d) 0.05.
Fig. 4 shows the SEM micrographs of [Ba1−x Y2x/3 ]
(Zr0.25 Ti0.25 )O3 ceramics prepared with different concentrations (x = 0, 0.01, 0.025 and 0.05) and sintered at 1673 K for
4 h.
A closer examination of the SEM micrographs revealed that the
Y content strongly modifies the microstructure of the material. Initially, when the BaCO3 TiO2 , ZrO2 and Y2 O3 (only as a doping)
powders are mixed and milled, its particle sizes are reduced to
favor the matter transport mechanism during the sintering process. However, mainly due to the milling stages, probably the
particles have irregular spherical shapes. When the powders are
submitted to the sintering process performed at 1673 K for 4 h, the
movement of atoms or molecules is driven by differences in curvature between the particles in contact [53]. In order to reduce
surface free energy, atoms supposedly move from particles with
smaller radius to those with larger radius. Particularly, for the
[Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics with concentrations of x = 0
(pure phase) and x = 0.01, it is possible that the matter transport
between several aggregated particles and the high anisotropy in
the grain boundary energies induced the formation of compact and
irregular polyhedral particles (Fig. 4(a and b)). The addition of Y
(x = 0, 025 and 0,05) into the matrix intensified the shrinkage and
densification rates, resulting in a mass more dense (Fig. 4(c and
d)). This phenomenon suggests that the formation of [YO6 ] clusters is able to influence in the microstructural stability. Possibly,
it promoted a rapid interdiffusion movement via grain-boundary,
favoring the formation of necks between the grains as well as its
growth.
Fig. 5 shows the temperature dependence of relative real
and imaginary dielectric permittivity performed at differ-
ent frequencies (from 1 kHz to 1 MHz) for the [Ba1−x Y2x/3 ]
(Zr0.25 Ti0.25 )O3 ceramics prepared with different concentrations
(x = 0, 0.01, 0.025 and 0.05) and sintered at 1673 for 4 h.
The literature [54] reports that the diffuse phase transition
verified in some materials is characterized by a broadening in
the εm with the frequency. In typical ferroelectric relaxors, such
as Pb(Nb2/3 Mg1/3 )O3 –PbTiO3 ceramics [55,56], the diffuse phase
transition is generally accompanied by dispersion in the frequency
measurements at temperatures lower than Curie point. It is wellknown that the dielectric permittivity of a typical ferroelectric
material above the Curie temperature (Tc ) follows the Curie–Weiss
law, which is described by:
ε=
C
(T − To )
,
(T > To )
(2)
where To is the Curie–Weiss temperature and C is the Curie–Weiss
constant.
Fig. 6 shows the inverse dielectric permittivity as a function
of temperature performed at different frequencies (from 1 kHz to
1 MHz) for the [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics prepared with
different concentrations (x = 0, 0.01, 0.025 and 0.05) and sintered
at 1673 for 4 h.
In this figure, a deviation from Curie–Weiss law can be seen in
all frequency range. According to the literature [57], the degree of
deviation (Tm ) from the Curie–Weiss law is defined as:
Tm = Tcw − Tm
(3)
where Tcw denotes the temperature where the dielectric permittivity starts to deviate from the Curie–Weiss law and Tm represents
the temperature of maximum dielectric permittivity. The Tcw was
T. Badapanda et al. / Materials Chemistry and Physics 121 (2010) 147–153
151
Fig. 6. Inverse dielectric permittivity as a function of temperature performed at different frequencies (from 1 kHz to 1 MHz) for the [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics
prepared with different concentrations: (a) x = 0, (b) 0.01, (c) 0.025 and (d) 0.05.
determined from the graph by the extrapolation of the reciprocal
dielectric constant in the paraelectric region.
The modified Curie–Weiss law [58,59] has been proposed by
several research groups to investigate the diffuseness of the ferroelectric phase transition, which is described by the following
equation:
1
1
(T − Tm )
=
−
εm
ε
C
(4)
The linear extrapolation was used to estimate the values,
which are listed in Table 1. As it can be seen in Fig. 7, the different values obtained at 100 kHz for all compositions suggest
that the [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics have a diffuse-type
phase transition. Also, it was observed that the gradual addition of
Y into the Ba(Zr0.25 Ti0.25 )O3 ceramics increases the values, i.e., it
intensifies the diffusivity. Besides the compositional fluctuations,
probably the diffusivity also occurs due to the structural disorder
associated to the distinct clusters ([TiO6 ], [ZrO6 ], [YO6 ], [BaO12 ])
where is the relaxation strength and C is a constant. The value
allows to obtain information on the diffuse phase transition. In this
case, for = 1 → the classical Curie–Weiss law is valid, for = 2 →
this law obeys a quadratic dependence and it describes a complete
diffuse phase transition (Table 1).
Fig. 7 shows the graph of log((1/ε ) − (1/εm )) as a function of log
(T − Tm ) performed at 100 kHz for the [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3
ceramics.
Table 1
Parameters obtained from temperature dependent dielectric studies at 100 kHz on
the composition of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics with different Y content.
[Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3
x = 0.0
x = 0.01
x = 0.025
x = 0.05
Tm (K)
To (K)
C (105 K)
Tm
Tcw
εm
273.1
307.5
2.1
88.3
361.4
5572.6
1.72
297.1
319.8
1.5
70.6
367.8
1262.3
1.65
228.2
265.2
2.5
79.5
307.7
2004.4
1.77
210.2
241.2
2.8
87
297.2
1297
1.83
Fig. 7. log((1/ε ) − (1/εm )) as a function of log(T − Tm ) performed at 100 kHz for the
different compositions of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics.
152
T. Badapanda et al. / Materials Chemistry and Physics 121 (2010) 147–153
Fig. 8. (1/Tm ) as a function of ln() for the [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics. The
symbols are experimental points, while the line is obtained by the Vogel–Fulcher
relation.
(Fig. 3b). In this case, the compound is able to present a microscopic heterogeneity with different local Curie points. Therefore,
the dielectric permittivity behavior suggests that this material has
a ferroelectric–relaxor phase transition.
Fig. 8 shows the graph of (1/Tm ) as a function of ln() for the
[Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3 ceramics.
The nonlinear nature indicates that the data can not be fitted by
the simple Debye equation. Therefore, the relaxation time of these
ceramics must be expressed by the Vogel–Fulcher equation [60,61]:
= 0 exp
−Ea
kB (Tm − Tf )
(5)
where 0 is the attempt frequency, Ea is the average activation
energy, kB is the Boltzman constant and Tf is the freezing temperature. The Tf is considered as the temperature where the dynamic
reorientation of dipolar cluster polarization can not be thermally
activated. In our work, the fitting parameters are displayed in
Table 2.
In this table, the fitting parameters are in good agreement with
the Vogel–Fulcher equation, suggesting that the relaxor behavior
of some materials is analogous to those observed in dipolar glasses
with polarization fluctuations above the static freezing temperature. Another important point is that the activation energy and the
pre-exponential factor are both consistent with thermally activated
polarization fluctuations. In fact, the empirical relaxation strength
with dispersion in the frequency measurements at Tm is defined as:
Tres = Tm(1 MHz) − Tm(10 kHz)
(6)
where Tres is derived from the dielectric measurements of the
ceramic compounds. In this work, it was found the following Tres
values for the different compositions of [Ba1−x Y2x/3 ](Zr0.25 Ti0.25 )O3
ceramics: 17.14 for x = 0.0; 11.44 for x = 0.01; 20.43 for x = 0.025
and 34.33 for x = 0.05.
Table 2
Fitting parameters obtained by the Vogel–Fulcher equation for the different compositions of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics.
[Ba1−x Y2x/3 ]
(Zr0.25 Ti0.75 )O3
x = 0.0
x = 0.01
x = 0.025
x = 0.05
Tf (K)
Ea (eV)
o (Hz)
128
0.1538
1.03 × 1011
143
0.1837
1.23 × 1011
108
0.0932
0.09245 × 1011
93
0.0853
0.08613 × 1011
Hence, the relaxor behavior noted in these ceramics can be
related to the many reasons, such as: microscopic compositions
fluctuation, the merging of micropolar regions into the macropolar
regions and/or local disorder caused by the strains [62]. In addition, the randomly distributed electrical fields in a strain field into
a mixed oxide system are considered the main reason responsible
for the relaxor property. The literature [63] describes that aliovalent
cations incorporated into a perovskite-type structure may behave
as donor or acceptor species, significantly affecting the electrical
properties of the material. Thus, Watanabe et al. [64] showed that
the addition of rare earth elements into the BaTiO3 matrix is able
to present up to three substitution stages. In the first two stages,
the doping ions can replace the original ions located on both A or
B-sites into the lattice. In the third stage occurs a substitution limit,
favoring the formation of secondary phases. On the basis of the
Watanabe’s results, there is a probability of the Y3+ ions occupy
both A or B-sites into the Ba(Zr0.25 Ti0.75 )O3 ceramics. Hence, in the
first stage, we believe that due to the Y3+ ions (0.086 nm) exhibit
an ionic radius smaller than those of Ba2+ ions (0.161 nm); they
occupy the B-sites and cause the distortion of the lattice [65]. Probably, this mechanism leads to the stronger interaction between the
atoms situated in B-sites with the oxygen atoms, increasing the Tc .
Also, it is possible to conclude that the concentration of Y was not
sufficient to get in the substitution limit, since the XRD patterns do
not show the existence of secondary phases, as Y2 O3 , into the lattice (Fig. 1). Moreover, the ionic radius of Y3+ ions is slightly higher
than those of Ti4+ (0.0605 nm) or Zr4+ (0.072 nm) [66]. In fact, this
replacement could result in weaker interactions between the B-site
atoms with the oxygen atoms, reducing the Tc .
4. Conclusions
In summary, [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics with different concentrations (x = 0, 0.01, 0.025 and 0.05) were prepared by
SSR. The XRD patterns showed that this material crystallizes in a
cubic phase for all compositions. Secondary phases (Y2 O3 ) were
not observed, suggesting that the Y3+ ions were incorporated into
the structure. The slightly reduction in the lattice parameter values with the increase of Y content was attributed to the distortion
caused by the replacement of B-sites occupied by Ba2+ ions by those
of Y3+ . It was explained by the differences between the atomic radii
of these two ions (Ba2+ ions → 0.161 nm and Y3+ ions → 0.086 nm).
The SEM micrographs revealed that the Y content induced a rapid
matter transport by means of grain-boundary, resulting in the
formation of necks between the grains. In terms of electric measurements, the reduction in the dielectric permittivity magnitude
and the shifting of εm values to higher temperatures suggested a
relaxor behavior for this material. The different values obtained
at 100 kHz for all compositions showed that the material exhibits a
diffuse-type phase. Also, the experimental Tm data revealed a good
agreement with the Vogel–Fulcher equation. The quantitative analysis based on the empirical parameters (Tm , Tres and Tcw ) confirmed the relaxor nature of [Ba1−x Y2x/3 ](Zr0.25 Ti0.75 )O3 ceramics.
Acknowledgements
The authors acknowledge the financial support of the Brazilian research financing institutions: CAPES, CNPq and FAPESP (No .
2009/50303-4). Special thanks to Professor Dr. Sanjeeb Kumar Rout
for consolidating the partnership of this research between Brazil
and India.
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