Journal of Crystallization Process and Technology, 2012, 2, 1-11
http://dx.doi.org/10.4236/jcpt.2012.21001 Published Online January 2012 (http://www.SciRP.org/journal/jcpt)
1
Determination of A.C. Conductivity of Nano-Composite
Perovskite Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel
Technique
M. Willander1, O. Nur1, M. Q. Israr1, A. B. Abou Hamad2, F. G. El Desouky 2, M. A. Salem2,
I. K. Battisha2*
1Department of Science and Technology, Campus Norrkoping, Linkoping University, Norrkoping, Sweden; 2Solid State Physics
Department, National Research Center (NRC), Giza, Egypt.
Email: *szbasha@yahoo.com
Received September 15th, 2011; revised October 25th, 2011; accepted November 6th, 2011
ABSTRACT
Nano-composite, perovskite Ba(1–x–y)Sr(x)TiFe(y)O3, denoted as (BSTF) in powder form was derived via sol-gel (SG)
method followed by sintering at fixed temperature 750˚C for one hour. The morphology and structure of the powder
samples were investigated by using X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning
electron microscope (SEM). The XRD characterization indicates formation of a tetragonal crystalline phase in the pure
BST. A well defined perovskite phase with nano-crystallite sizes equal to about 32 nm was achieved from XRD for
B10ST20F sample, while TEM study confirmed the obtained XRD results giving the following crystallite size value
about 29.82 nm for the same sample. The dielectric A.C. conductivity was evaluated as a function of temperature and
frequency ranging from 42 Hz up to 1 MHz.
Keywords: Sol-Gel; Dielectric Permittivity; A.C. Conductivity; Nano-Structure BaSrTiO3 (BST); TEM; XRD and SEM
1. Introduction
Barium titanate, which is the host material for doping with
the Sr has been extensively employed in several industrial
applications, including dynamic random access memory
(DRAM) capacitors, microwave filters, infrared detectors
and dielectric phase shifters, due to its excellent ferroelec-
tric, dielectric, piezoelectric and pyroelectric properties
[1-5]. It was previously reported that for the ABO3 pero-
vskite, different A-site and B-site dopants (where A = Ca,
Sr, La; B = Nb, Ta, Zr) were used to modify the electrical
properties of BaTiO3 based compositions [6-9].
Recently, barium strontium titanate (BST) attracted much
attention because of its strong dielectric nonlinearity un-
der bias electric field and linearly adjustable Curie tem-
perature with the strontium content over a wide tempera-
ture range [9-11]. The desired properties make BST a pro-
mising candidate material for tunable microwave dielec-
tric devices [12,13]. Ferroelectric and dielectric properties
of BST ceramics are strongly dependent on the sintering
conditions, grain size, porosity, doping amount and struc-
tural defects [14-16].
Fe-doped (Ba1–xSrx)TiO3 is usually prepared by many
processes such as ball milling, solid-state reaction and sol
gel, which is used in this work etc. either in powder or thin
film forms. It was suggested previously that in Fe-doped
(Ba1–xSrx)TiO3 micro-structural and dielectric properties
were modified by controlling the Fe concentration (0.01
x 0.20 mol%) with fixed Sr concentrations [1-8]. Ba-
rium strontium titanate (BST) with high dielectric constant
(ε) attracted much interest as materials for environmen-
tally applications (dielectric for capacitors, actuators, etc.).
It is a perovskite-based ferroelectric, and one of the most
studied ferroelectric materials, exhibiting normal, first-
order phase transition behavior. Previous studies on the
dielectric properties of BaxSrl–xTiO3 ceramic solid solu-
tions have shown that the compositions with x 0.2 ex-
hibited normal ferroelectric behavior while the relaxation
characteristics have been observed in the SrTiO3 rich
region (x < 0.2). The loss factor in these materials is re-
duced with the addition of a proper substitute. Few authors
have reported the substitution of Fe in BST and strontium
titanate where Fe3+ ion substitutes Ti4+ in BST and reduces
the dissipation factor due to domain wall motion [9-20].
The purpose of the present work is to determine the
temperature and the frequency dependence on dielectric
and A.C. conductivity of the prepared nano-composite
BST and BSTF powders samples. The structure and the
morphology of the prepared samples will be evaluated by
*Corresponding author.
Copyright © 2012 SciRes. JCPT
Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
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using XRD, SEM and TEM.
2. Materials and Methods
2.1. Samples Preparation
Ba(1–x)Sr(x=0.1)TiO3 and Ba(1–x–y)Sr(x)TiFe(y)O3 where (x =
0.1 and y = 0.01, 0.03, 0.05, 0.15 & 0.20) denoted as
(BST) and BST(1 - 0.20)F, respectively powder systems
were prepared by a modified sol-gel method. BST system
has the following different Sr contents and symbols: (a)
B3ST = 0.03 mol% Sr, B10ST= 0.1 mol% Sr, B15ST =
0.15 mol% Sr and B20ST = 0.2 mol% Sr. While the
Ba(1–x–y)Sr(x)TiFe(y)O3, where (x = 0.1 and y = 0.01, 0.03,
0.05, 0.10, 0.15 & 0.20) has the following different Fe
contents and symbols, (a) B10ST1F = 0.1 mol% Sr &
0.01 mol% Fe, (b) B10ST3F = 0.1 mol% Sr & 0.03
mol% Fe, ( c ) B10ST5F = 0.1 mol% Sr & 0.05 mol% Fe,
(d) B10ST10F = 0.1 mol% Sr & 0.1 mol% Fe and (e)
B10ST20F = 0.1 mol% Sr & 0.20 mol% Fe, respectively.
BaSrTiO3 doped with different concentrations of stron-
tium and iron in powder form have been prepared using
barium acetate (Ba(Ac)2) (99%, Sisco Research Labora-
tories PVT.LTD, India) and titanium butoxide (Ti(C4H9O)4),
(97%, Sigma-Aldrich, Germany) as starting materials. Ace-
tyl acetone (AcAc, C5H8O2), (98%, Fluka, Switzerland)
acetic acid (HAc)-H2O mixture (96%, Adwic, Egypt)
were adopted as solvents of (Ti(C4H9O)4), and Ba(Ac)2,
respectively. Strontium bromide was added to the pre-
cursor with different molar ratios. Iron nitrate was added
to the final solution of B10ST with different concentra-
tions. Densification of the gel was achieved by sintering
in air for one hour at 750˚C, in a muffle furnace type (Car-
bolite CWF 1200).
2.2. Characterization
X-ray diffraction (XRD) patterns were recorded with a
Philips X-ray diffractometer using monochromatic CuK1
radiation of wavelength
= 1.5418 Å from a fixed source
operated at 40 kV and 30 mA. The crystallite size (G) was
determined from the Scherrer’s equation G = K
/D cos
,
where K is the Scherer constant (0.9),
is the wavelength
and D is the full width (in radians) of the peak at half ma-
ximum (FWHM) intensity.
The microstructure and the morphology of the pre-
pared samples were characterized by using JEOL trans-
mission electron microscope (TEM), model: Jeol 1230"
with magnification up to 600 k×, giving a resolution down
to 0.2 nm. We performed the measurement at an accelera-
ting voltage of 100 kV. A computerized LRC bridge (Hi-
oki model 3531 Z Hi Tester) was used to measure the
electrical properties of the samples. The dielectric constant
for the investigated samples was studied from room
temperature up to 250˚C at different frequencies ranging
from 42 Hz up to 1 MHz. The samples used in the dielec-
tric measurements were in disk form, having 10 mm in dia-
meter and 3 mm in thickness, pressed using a pressure of
10 Ton at room temperature. Then, silver paste was coated
to form electrodes on both sides of the sintered ceramic
specimens in order to ensure good contacting. The elec-
trical measurements were carried out by inserting the sam-
ple between two parallel plate conductors forming cell
capacitor. Then, the whole arrangement was placed in to
non-inductive furnace for heating the samples with con-
stant rate [1].
0
Cd
A
(1)
tan δ


(2)
where,
is the permittivity,
 is the dielectric loss
and tanδ is the loss tangent and A is the area of the elec-
trode.
The A.C. resistivity of the prepared samples was esti-
mated from the dielectric parameters. As long as the pure
charge transport mechanism is the major contributor to the
loss mechanism, the resistivity (ρ) can be calculated us-
ing the following relation:
0
=1tanCm

 (3)
where
= 2πf,
is the angular frequency and f is the
frequency of the applied electric field in Hertz.
s = 2πfdCtanA
(4)
where σ is the A.C. conductivity, f is the operating fre-
quency, d is the thickness of the dielectrics, tanδ is the
dielectric loss, C is the capacitance and A is the area of the
electrode.
3. Results and Discussion
X-ray diffraction was performed to characterize the crys-
tallinity and phase of the nano-particles. Figures 1 and 2
show the XRD patterns of pure BS10T and BST5&20Fe,
respectively. The XRD patterns indicate that all the sam-
ples are polycrystalline and exhibit tetragonal perovskite
structure with (110) as a major peak, (JPCDS No 44-
0093). The inset in Figure 1 shows the splitting in the
peak extended in the range between 2θ˚ equal 43.5 and
47 which, is consistent with the tetragonal phase.
Figure 2 shows the XRD patterns of BST5&20F, sin-
tered for one hour at 750˚C. New hematite phase α
Fe2O3 was began to appear in the B10ST20F pattern.
Figure 3 shows the splitting of the peak in the 2θ
range between 43.5˚ and 47˚, which was shifted towards
a lower 2θ˚ value by increasing the iron oxide concentra-
tion. The splitting was appeared well in B10ST5F sample
while it began to be weaker in B10ST20F sample but the
tetragonal phase is still present in it. The obtained data
imply the presence of the tetragonal structure phase from
XRD in pure BST and B10ST5&20F samples, Card
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
Copyright © 2012 SciRes. JCPT
3
Figure 1. XRD patterns of B10ST powder samples sintered at 750˚C for 1 hour, the inset is of the expansion of the angle 2θ˚
ranges between 43.5˚ up to 47˚, respectively.
Figure 2. XRD patterns of (a) B10ST5F and (b) B10ST20F powders s samples sintered for one hour at 750˚C for one hour.
Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
4
Figure 3. The expansion of the 2θ˚ in the range between
43.5˚ up to 47˚ of (a) B10ST5F and (b) B10ST20F.
number [44-0093] (tetragonal phase).
Weak lines corresponding to the residual carbonates
phases, such as BaCO3, SrCO3 and (Ba, Sr)CO3 were
appeared [16]. The full width at half maximum of (110)
peak increases by increasing iron oxide concentration
which, indicated the decrease in the crystallite sizes from
36.5 nm for pure B10ST to 33.5 and 32 nm for both
doped samples B10ST5F and B10ST20F, respectively.
The average crystallite size decreased as the dopand con-
centration was increased, which could be attributed to the
fact that the particle growth was hindered by the oxygen
vacancies, lattice distortion as well as the internal stress
arising from the substitution of Ti with Fe [18,19].
Figure 4 shows the representative TEM of BS10T20F
thermally synthesized in air for 1 h at 750˚C. Some de-
gree of agglomerates has been found in the clusters con-
sisting of many small grains [20,21]. The calculated av-
erage crystallite size from TEM was 29.82 nm, which is
nearly equal to the value obtained from XRD (32 nm) for
the same sample. The TEM was used to confirm the data
obtained from XRD patterns and that the sample is in
nano-scale.
Surface morphologies obtained through Scanning Elec-
tron Microscope (SEM) of the pure B(3, 5 & 0.20)ST and
doped samples B10ST(3, 5 & 20) Fe powder samples sin
Figure 4. TEM micrographs of B10ST20F, poer samples sintered at 750˚C for one hour. wd
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
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tered at 750˚C for one hour were shown in Figures 5(a)-
(c) and Figures 6(a)-(c), respectively. The images in Fig-
ure 5 shows comparatively more accumulated particles
with higher density showing increase in grain growth at
higher Sr content and the particles have a well-defined
shape.
Images in Figure 6 clearly show that the additive of
iron oxide has leads to a grains refining, whereas their lack
induce a strong effect of exaggerated grain growth by the
formation of large faceted grains, and higher density than
the pure samples was observed due to the well dispersion
(a)
(b)
(c)
Figure 5. The SEM micrograph of (a) (B3ST), (b) (B5ST)
and (c) (B20ST) powder samples sintered at 750˚C for one
hour.
(a)
(b)
(c)
Figure 6. The SEM micrograph of (a) (B10ST3F), (b) (B10-
ST10F) and (c) (B10ST20F) powder samples sintered at
750˚C for one hour.
of iron oxide inside the pure sample. This can be corre-
lated with the predominant XRD peaks as obtained for
the doped samples in which new hematite phase appeared
at higher iron concentration [19].
To investigate the dielectric properties of our two BST
systems (doped and un-doped samples), we fabricated ca-
pacitors using silver paste as an electrode. For doped sam-
ples B10ST10F and B10ST20F a typical Curie-Weiss re-
sponse was registered and the temperature dependence of
their relative permittivity were shown in Figures 7(a) and
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
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(b). It was found that the dielectric constant of each sam-
ple has its own maximum corresponding to the Curie
point temperature (Tc) where the (Tc) decreases by dop-
ing the sample with 10 and 20 mol% of iron oxide giving
the following values 80˚C and 50˚C, respectively as
shown in Figures 7(a) and (b) [22] This might be due to
phase transformation from the ferroelectric (polarized
state) to the para-electric (unpolarized sate).
Figure 8 shows the frequency dependence of the di-
electric permittivity
(a and c) and the loss tangent
tanδ (b and d) of B10ST10F and B10ST20F samples as a
function of the frequency during heating in the range
starting from 25˚C up to 250˚C. The same behavior from
the pure BST system mentioned previously by our team
work was observed [16], where the dielectric constant
(
) decreased with increasing frequency showing an
anomalous dispersion. Such dispersion in (
) is accom-
panied by a relaxation peak in tanδ. The intensity of
(a)
(b)
Figure 7. Temperature dependence of the dielectric constant
at various frequencies for (a) B10ST10F and (b) B10ST20F.
this peak is slightly increased and its maximum shifted to
lower frequencies with increasing the temperature for
B10ST10F and B10ST20F. Then it disappeared at a
temperature above 70˚C and 50˚C, respectively for the
two samples. At these two mentioned temperature, Curie
temperature (Tc), abrupt change in dielectric properties can
be occurred. Above Tc, (
) showed markedly decrease
leading to ferroelectric-paraelectric phase transition.
The Curie temperature of the doped samples were
found to be decreased from 80˚C to 50˚C for the doped
barium strontium titanate B10ST10F and B10ST20F, res-
pectively, indicating ferroelectric-para-electric phase tran-
sition. A notable decrease in dielectric constant by increas-
ing the iron content was observed due to the fact that iron
oxide dopants may inhibit grain growth and therefore re-
duction of grain size was occurred. Consequently, the die-
lectric properties of the B10ST(10 and 20)F are decreased.
Another interpretation for such decrease related to the fact
that iron oxide has different lattice constant which add a
stress in to the lattice [23-25].
By focusing our study on the A.C conductivity one can
observe from Figure 9 that the A.C. conductivity increases
by increasing the frequency values. The conductivity (σ)
of the samples was calculated using the formula σ = 2πfdC
tanδ/A as shown in Equation (4) Section 2. At 30˚C and
100˚C the A.C. conductivity was found to decrease by
increasing the Sr concentration from 10 up to 15 mol%,
and by doping with different concentrations of iron ox-
ide, while at 120˚C the doped samples with Sr have
higher conductivity as shown in Table 1. The decrease
in conductivity by doping with different concentrations
of Sr and Fe may be primarily due to the decrease in
tanδ loss with Sr and Fe substitution as stated earlier
[26], or may be partly due to the decrease in the grain
size and hence the increase in the grain boundary areas/
resistance with Sr and Fe substitution. Grain boundary
areas are highly resistive in oxide ceramics. Smaller
grain sized ceramics has a larger grain boundary areas
and hence higher resistivity.
This result is consistent with the previously reported
results; where it was confirmed that the intrinsic capabil-
ity of the perovskite structure (ABO3) to host ions of dif-
ferent sizes, with doping in small amounts with acceptor
ions could greatly affect the dielectric properties [27-30].
However, the effect of the specific impurity on the elec-
trical conductivity depends on the substitution site so the
trivalent ion like Fe3+ behaves as an acceptor when sub-
stitution occurs at the Ti site or as a donor when it sub-
stitutes at the Ba site. Acceptor dopants are defined as ions
with a lower valence than the ions that they replaced (e.g.
Fe3+ for Ti4+). Chan and Smyth [30] postulated that ac-
ceptor impurities are mostly compensated by oxygen va-
cancies.
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
Copyright © 2012 SciRes. JCPT
7
(a)
(b)
(c)
Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
8
(d)
Figure 8. The frequency dependence of the dielectric permittivity ε' (a and c), and the loss tangent tanδ (b and d) of B10-
ST10F and B10ST20F.
(a)
(b)
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
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(c)
(d)
(e)
Figure 9. The A.C. conductivity of (a) B10ST1F; (b) B10ST5F ; (c) B10ST10F; (d) B10ST20F and (e) B10ST.
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Determination of A.C. Conductivity of Nano-Composite Perovskite
Ba(1–x–y)Sr(x)TiFe(y)O3 Prepared by the Sol-Gel Technique
Copyright © 2012 SciRes. JCPT
10
Table 1. The A.C. conductivity of B10ST, B15ST, B10ST5F, B10ST10F and B10ST20F at 3 different temperature 30˚C,
100˚C and 120˚C.
σ ( )cm–1
RTC (30)˚C
1 KHz 10 KHz 50 KHz
B10ST 2.44E–05 3.77E–05 7.83E–05
B15ST 6.98E–06 1.05E–05 1.96E–05
B10ST5F 1.76E–05 2.63E–05 4.35E–05
B10ST20F 1.64E–05 2.63E–05 3.84E–05
RTC 100˚C
1 KHz 10 KHz 50 KHz
B10ST 3.10E–06 9.67E–06 2.38E–05
B15ST 1.20E–05 2.29E–05 3.20E–05
B10ST5F 8.25E–07 1.81E–06 4.50E–06
B10ST20F 1.37E–06 3.82E–06 7.89E–06
RTC 120˚C
1KHz 10KHz 50KHz
B10ST 5.12E–07 2.24E–06 1.09E–05
B15ST 1.77E–06 1.08E–05 3.46E–05
B10ST5F 6.78E–07 1.37E–06 3.21E–06
B10ST20F 8.38E–07 2.42E–06 5.46E–06
4. Conclusion
Using the sol-gel method, nano-structure pure B(3, 5 &
20)ST and doped B10ST(1-20)F powder systems have
been successfully prepared. Tetragonal phase with un-
wanted amount of BaCO3 and SrCO3 have been obtained
for both the pure and doped with 5 and 20 mol% of iron
oxide systems. In addition a well defined perovskite phase
with nano-crystallite sizes for B10ST, B10ST5F and
B10ST20F equal to 36.5, 33.5 and 32 nm, respectively
were achieved. Doping the prepared samples with dif-
ferent concentrations of iron oxide is effective to de-
crease the crystallite size. TEM micrograph has used to
confirm and complement the XRD results giving the fol-
lowing crystallite size value 29.82 nm for B10ST20F.
The dielectric properties of both BST and BSTF systems
in the ferroelectric phase showed strongly frequency and
temperature dependence. At 30˚C the A.C. conductivity
was found to decrease by increasing both the Sr concen-
tration from 10 up to 15 mol%, and the iron oxide con-
centrations from 5 up to 20 mol%, due to the decrease in
the grain size and hence the increase in the grain bound-
ary areas/resistance with Sr and Fe substitution.
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