Materials Science s a nd Applications, 2011, 2, 1593-1600
doi:10.4236/msa.2011.211213 Published Online November 2011 (http://www.SciRP.org/journal/msa)
1593
Structural and Electrical Characteristics of
Ba(Fe0.5Nb0.5)O3-SrTiO3 Ceramic System
Narendra Kumar Singh1*, Pritam Kumar1, Ajay Kumar Sharma1, Ram Naresh Prasad Choudhary2
1University Department of Physics, V. K. S. University, Bihar, India; 2Physics Department, ITER, SOA University, Bhubnesher
(Orisa), India.
Received August 27th, 2011; revised October 8th, 2011; accepted October 19th, 2011.
ABSTRACT
A complex structure of barium iron niobate, Ba(Fe0.5Nb0.5)O3 (BFN) and strontium titanate SrTiO3 (ST) was fabricated
by a solid-state reaction method. The phase formation of Ba(Fe0.5Nb0.5)O3-SrTiO3 was checked using X-ray diffraction
(XRD) technique. The X-ray structural analysis of BFN and BFN-ST ceramics, showed the formation of single-phase
compound in the monoclinic system, which is a distorted structure of an ideal cubic perovskite. Careful examination of
microstructures of the individual compounds of the system was done by the scanning electron micrograph (SEM), and
confirms the polycrystalline nature of the systems. Detailed studies of dielectric and electrical impedance properties of
the systems in a wide range of frequency (100 Hz - 5 MHz) and different temperatures (30˚C - 285˚C) showed that these
properties are strongly dependent on temperature and frequency.
Keywords: Dielectrics, Perovskite Oxides, X-Ray Diffraction, Scanning Electron Micrograph
1. Introduction
Complex perovskite with general formula ABO3 (A =
mono-divalent, B = trid to hexavalent) are widely used
for detectors, sensors, actuators, multi-layer ceramic ca-
pacitor (MLCC), computer memories, pyroelectric de-
tectors, wireless communication systems, microelectron-
ics, global positioning systems and other electronic de-
vices. Ferroelectric perovskites have been the subject of
extensive studies due to their promising electrical char-
acteristic which has a potential usefulness in fundamental
research and technological applications. Investigation of
the electrical properties of these materials is desirable to
predict their suitability for electronic applications. Vari-
ous relaxation processes seem to coexist in complex
perovskite ceramics, which contain a number of different
energy barriers due to point defects appearing during
their fabrication. Therefore, the departure of the response
from an ideal Debye model in ceramic samples, resulting
from the interaction between dipoles, cannot be disre-
garded. A method of predicting the relaxation behavior
of a perovskite is through electric modulus theory [1].
The dielectric constant of a material (dielectric) ch-
anges due to the change of polarization by an applied el-
ectric field. This change in polarization is time dependent.
Because of the resistance (resistivity) to the motion of the
atoms in the dielectric, there is always a delay between
changes in the field and changes in the polarization,
which gives the dissipation factor tanδ and is propor-
tional to the energy absorbed per cycle by the dielectric
from the field [2].
Alternating current (AC) impedance spectroscopy is
an appropriate method to study 1) the properties of the
intragranular and interfacial regions and their interrela-
tions, 2) their temperature and frequency dependent
phenomena in order to separate the individual contribu-
tions from the total impedance and 3) their interfaces
with electronically conducting electrodes [3-6]. AC im-
pedance spectroscopy allows measurement of the ca-
pacitance (C) and tangent loss (tanδ) over a frequency
range at various temperatures. From the measured ca-
pacitance and tangent loss, four complex dielectric func-
tions can be computed: impedance (Z*), permittivity (*),
electric modulus (M*) and admittance (Y*). Studies of
electrical data in the different functions and forms allow
different features of the materials to be recognized.
Materials having a diffuse phase transition have at-
tracted the most attention due to their broad maximum in
the temperature dependence of their dielectric constant.
The high value of the dielectric constant over a very wide
temperature interval is due to disorder in the distribution

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System
1594 0.50.5 33
of B-site ions in the perovskite unit cell. This may lead to
composition fluctuations and, as a consequence, to dif-
ferent local Curie temperatures in the different regions of
the ceramic [7].
Recently, high dielectric permittivity (
 ') has been re-
ported for ternary perovskite BaFe0.5Nb0.5O3 (BFN) of
certain compositions. Many researchers have studied
BFN, including Saha and Sinha [8], Intatha et al. [9],
Fang et al. [10], Raevski et al. [11] Nedelcu et al. [12],
Tezuka et al. [13], Yokosuka et al. [14] and Rama et al.
[15]. They have reported that the BFN-based electroce-
ramics exhibit a relaxor behavior by showing very attrac-
tive dielectric and electric properties over a wide range of
temperatures. However, there still exist considerable de-
bates concerning the physical mechanisms governing
their electrical behavior [9]. In the present work,
Ba(Fe0.5Nb0.5)O3 (BFN) and strontium titanate SrTiO3
(ST) was fabricated by a solid-state reaction method. The
dielectric characteristics of BFN(a), BFN-ST5(b) and
BFN-ST10(c) ceramics are evaluated in broad tempera-
ture and frequency ranges.
2. Experimental Procedures
Complex perovskite oxides (1-x)Ba(Fe0.5Nb 0.5)O3-xSrTiO3,
(where x = 0, 0.05 and 0.10; hereafter abbreviation as
BFN(a), BFN-ST5(b) and BFN-ST10(c) respectively)
were prepared by a solid-state reaction technique. High
-purity (≥99.9%) ingredients: BaCO3, SrCO3, TiO2,
Nb2O5 and Fe2O3 ((all from M/s Merck specialities pri-
vate limited), were used for the preparation of BFN(a),
BFN-ST5(b) and BFN-ST10(c) ceramics. These chemi-
cals were taken in stoichiometric ratio, and mixed in the
presence of acetone for 5 h. The finely mixed powder of
BFN(a), BFN-ST5(b) and BFN-ST10(c) were calcined at
1200˚C for 8 h. The calcined powder of above mentioned
ceramics were regrinded and used to make pellet of di-
ameter ~10 mm and thickness 1 - 2 mm using polyvinyl
alcohol as binder. The pellets were sintered at 1250˚C for
5 h and then brought to room temperature under con-
trolled cooling. The formation and quality of the com-
pounds were checked with X-ray diffraction (XRD)
technique. The frequency dependence of the capacitance
and conductance is measured using an LCR meter in the
temperature range from 30˚C to 285˚C and in the fre-
quency range from 100 Hz to 5 MHz. The ac electrical
conductivity 0ac

 
  were obtained from the tem-
perature dependence of the real (ε′) and imaginary (ε″)
components of the complex dielectric constant ε* =
(ε′-jε″). The X-ray powder diffraction pattern of the sam-
ple is taken at room temperature using a X-ray powder
diffractometer (Rigaku Miniflex, Japan) using Cukα ra-
diation (λ = 1.5418 Å) in a wide range of Bragg angles
2θ (20˚ ≤ 2θ ≤ 80˚) with scanning rate 2˚/min. The mi-
crographs are recorded using scanning electron micros-
copy JEOL-JSM-5800 to study the surface morphol-
ogy/microstructure of the sintered pellets.
3. Results and Discussion
The room temperature X-ray diffraction (XRD) patterns
of BFN(a), BFN-ST5(b) and BFN-ST10(c) ceramics is
compared in Figure 1. The nature of XRD patterns ap-
pears to confirm the formation of single-phase with
monoclinic crystal structure of the compounds. All the
reflection peaks of the XRD pattern of the samples were
indexed, and the lattice parameters were determined in
the monoclinic crystal systems using a computer program
“POWDMULT” [16].
On the basis of best agreement between the observed
(obs.) and the calculated (cal.) d-spacing


. .minimum
obs cal
ied dd 
, all the compounds
were found to be in monoclinic crystal system. The room
temperature SEM (scanning electron microscope) micro-
graphs of sintered pellets of BFN(a), BFN-ST5(b) and
BFN-ST10(c), ceramics are compared in Figure 2. The
nature of the micrographs exhibits the polycrystalline
texture of the material having highly distinctive and
compact rectangular/cubical grain distributions. Careful
examination (scanning) of the complete surface of the
sample exhibits that the grains are homogeneously dis-
tributed through out the surface of the sample. The aver-
age grain size of BFN(a), BFN-ST5(b) and BFN-ST10(c),
was around ~ 2 - 3 µm.
The logarithmic angular frequency dependence of the
dielectric constant (ε′) of BFN(a), BFN-ST5(b) and
BFN-ST10(c), ceramics at 30˚C and 130˚C are plotted in
Figure 3. At 30˚C, the dielectric constant (ε′) has a value
of 367 for BFN(a), 7125 for BFN-ST5(b) and 23153 for
Figure 1. X-ray diffraction patterns of BFN(a), BFN-ST5(b)
and BFN-ST10(c), ceramics, at room temperature.

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System1595
0.50.5 33
BFN
(a)
BFN-ST5
(b)
BFN- ST1 0
(c)
Figure 2. SEM micrographs of BFN(a), BFN-ST5(b) and
BFN-ST10(c) ceramics at room temperature at 1 µm mag-
nification.
Figure 3. Frequency dependence of dielectric constant ()
of BFN(a), BFN-ST5(b) and BFN-ST10(c) ceramics, at 30˚C
and 130˚C.
BFN-ST10(c) at 100 Hz, and gradually decreases as fre-
quency increases, But at 130˚C, the value of ' in the low
frequency region (below 1 kHz), increases significantly
for BFN(a) and BFN-ST5(b) ceramics.
This behavior is very much consistent with that of
common ferroelectrics. The higher values of
 ' at lower
frequencies are due to the presence of all different types
of polarizations (i.e., dipolar, atomic, ionic, electronic
contribution) in the material. At high frequencies, how-
ever, some of the above-mentioned polarizations may
have less contribution in
 '. This behavior is also found in
other compounds studied by us [17-22].
The high value of
 ' in the low frequency region has
been explained using Maxwell-Wagner (MW) polariza-
tion effect. Thus high values of permittivity are not usu-
ally intrinsic, but rather associated with heterogeneous
conduction in the grain and grain boundary of the com-
pounds. That is due to the grains of the sample are sepa-
rated by more insulating intergrain barriers, as shown in
a boundary layer capacitor [23].
The logarithmic angular frequency dependence of the
loss tangent (tanδ) of above mentioned ceramics at 30˚C
and 130˚C are plotted in inset of Figure 4. It is observed
that (tanδ)max maximum increases as temperature in-
creases from 30 to 130˚C, indicating that the concentra-
tion of conduction electrons increases as temperature due
to thermal activation [24].
Temperature dependence of dielectric constant (
 ′) and
tangent loss (tanδ) of BFN(a), BFN-ST5(b) and BFN-
ST10(c), ceramics is shown in Figure 5 and Figure 6
respectively at selected frequencies (1 and 20 kHz), re-
spectively. The dielectric constant (
 ′) is found to in-
crease with rise in temperature at selected frequency for
BFN(a) ceramics. One possibility for this behavior is that

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System
1596 0.50.5 33
Figure 4. Variation of tanδ with frequency of BFN(a),
BFN-ST5(b) and BFN-ST10(c) ceramics, at 30˚C and 130˚C.
Figure 5. Variation of dielectric constant (  ) with tempera-
ture of BFN(a), BFN-ST5(b) and BFN-ST10(c) ceramics at
1 kHz and 20 kHz.
Figure 6. Variation of tangent loss (tanδ) with temperature
for BFN(a), BFN-ST5(b) and BFN-ST10(c) ceramics at 1
kHz and 20 kHz.
it is due to the increased conductivity in the samples
caused by the presence of Fe2+ in sintered BFN (a) ce-
ramics, as suggested by Ananta and Thomas [25]. The
concentration of Fe2+ ions is known to be very sensitive
to temperature, and it increases as temperature increases
[26]. It is known that the co-existence of Fe2+ and Fe3+
ions on equivalent crystallographic sites can give rise to
an electron-hopping conduction mechanism. But for
BFN-ST5(b) and BFN-ST10(c) ceramics, the dielectric
constant increased with increasing temperature and be-
come broad curve from 180˚C onward. In addition, the
dielectric constant was found to decrease with increasing
frequency. This behavior may be due to fact that the di-
poles are able to follow the applied voltage at low fre-
quency, but they not follow to the field at higher fre-
quency.
From Figure 6, it is clear that in the low temperature
region, tanδ is almost constant up to a certain tempera-
ture and then increases faster up to a highest temperature
(~282.5˚C) in BFN(a), BFN-ST5(b) and BFN-ST10(c),
ceramics.
The logarithmic angular frequency dependence of Z′
and Z″ of BFN(a), BFN-ST5(b) and BFN-ST10(c) ce-
ramics, at several temperatures between 120˚C and
270˚C is plotted in Figure 7. At lower temperature, Z'
(BFN (a)), Z′ (BFN-ST5(b)) and Z′ (BFN-ST10 (c)) de-
creases monotonically with increasing frequency up to
certain frequency and then becomes frequency inde-
pendent. At higher temperatures, Z′ (BFN (a)), Z′ (BFN-
ST5 (b)) and Z' (BFN-ST10 (c)) is almost constant and
for even higher frequencies decreases sharply.
The higher values of Z′ (BFN (a)), Z′ (BFN-ST5 (b))
and Z' (BFN-ST10 (c)) at low frequencies and low tem-
peratures means the polarization is larger. The tempera-
tures where this change occurs vary in the material with
frequencies. This also means that the resistive grain
boundaries become conductive at these temperatures.
This also shows that the grain boundaries are not relaxing
even at very high frequencies even at higher tempera-
tures.
At lower temperatures Z″ (BFN (a)), Z″ (BFN-ST5 (b))
and Z″ (BFN-ST10 (c)) decreases monotonically sug-
gesting that the relaxation is absent. This means that re-
laxation species are immobile defects and the orientation
effects may be associated. As the temperature increases,
the peak of Z″ (BFN-ST5 (b)) and Z″ (BFN-ST10 (c))
starts appearing. The peak shifts towards higher fre-
quency with increasing temperature showing that the
resistance of the bulk material is decreasing. Also the
magnitude of Z″ (BFN-ST5 (b)) and Z″ (BFN-ST10 (c))
decreases with increasing frequencies. This would imply
that relaxation is temperature dependent, and there is
apparently not a single relaxation time. There by relaxa-

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System1597
0.50.5 33
Figure 7. Variation of Z′ and Z″ with frequency of BFN(a),
BFN-ST5(b) and BFN-ST10(c) ceramics at various tem-
peratures.
tion processes involved with their own discrete relaxation
time depending on the temperature. Also it is evident that
with increasing temperature, there is a broadening of the
peaks and at higher temperatures, the curves appear al-
most flat.
Complex impedance spectrum Z″ vs. Z′ (called as
Cole-Cole plot) of BFN(a), BFN-ST5(b) and BFN-
ST10(c) ceramics, at 220˚C is shown in Figure 8. Only
one semicircular arc is observed in the Cole-Cole plot
confirms that the polarization mechanism in BFN(a),
BFN-ST5(b) and BFN-ST10(c) ceramics. This electrical
behavior can be represented in terms of an equivalent
circuit (Figure 8 BFN (a) inset). The semicircle has their
center located away from the real axis, indicating the
presence of relaxation species, and non-Deby type of
relaxation process occurs in the materials. The appear-
ance of single semicircle in the impedance pattern at
220˚C suggests that the electrical process occurring in
the material has a single relaxation process possibly due
to the contribution for bulk material only.
Figure 9 shows the ac conductivity of the BFN(a),
BFN-ST5(b) and BFN-ST10(c) ceramics, as a function
of frequency at different temperatures. The ac conductiv-
ity of the system depends on the dielectric properties and
sample capacitance of the material. The two plateaus
separated by frequency region are observed in BFN (a)
ceramics. The low-frequency plateau represents the total
conductivity whereas the high-frequency plateau repre-
sents the contribution of grains to the total conductivity.
The presence of both the high and low frequency pla-
teaus in conductivity spectra suggests that the two proc-
esses are contributing to the bulk conduction behavior.
One of these processes relaxes in the higher frequency
region and contribution of the other process appears as a
plateau in the higher frequency region [27]. The conduc-
tivity shows dispersion which shifts to higher frequency
side with the increase of temperature. The strong fre-
quency dependent conductivity has been found above (10
kHz) for BFN-ST5(b) and BFN-ST10(c) with the fre-
quency independent conductivity below 10 kHz which is
a typical feature of perovskite at elevated temperature
(>180˚C).
4. Conclusions
In this work, we reported structural, dielectric and im-
pedance properties of barium iron niobate, Ba (Fe0.5
Nb0.5)O3 (BFN) and strontium titanate SrTiO3 (ST) pre-
pared by a high-temperature solid-state reaction method.
Preliminary structural analysis suggests that formation of
single-phase compound in the monoclinic system. De-
tailed studies of electrical (dielectric, impedance and
conductivity) properties exhibited a strong frequency
dependent dielectric dispersion of the compound.

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System
1598 0.50.5 33
Figure 8. Complex plane impedance plot of BFN(a),
BFN-ST10(b) and BFN-ST5(c) at 220˚C and equivalent
circuit (inset of Figure 8 (BFN (a))).
Figure 9. Variation of ac with angular frequency for
BFN(a), BFN-ST5(b) and BFN-ST10(c) ceramics, at various
temperatures.

Structural and Electrical Characteristics of Ba(FeNb )O -SrTiO Ceramic System1599
0.50.5 33
The microstructure of the ceramics was examined by the
scanning electron microscopy (SEM), and shows the
polycrystalline nature of the samples with different grain
sizes.
5. Acknowledgements
The authors are grateful to DRDO, for providing finan-
cial assistance for this Research work.
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