EFFECT OF Sr2+DOPING ON THE STRUCTURAL, THERMAL, DIELECTRIC AND ELECTRICAL PROPERTIES OF La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4}CATHODE FOR SOFCS

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Rasayan J. Chem., 14(2), 1019-1027(2021)
http://dx.doi.org/10.31788/ RJC.2021.1426153
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EFFECT OF Sr2+DOPING ON THE STRUCTURAL, THERMAL,
DIELECTRIC AND ELECTRICAL PROPERTIES OF
La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4}CATHODE FOR SOFCS
Manokamna1,, Surinder Paul1, A. Singh2, K. L. Singh3, G. Bhargava1
and A. P. Singh1
1Department of Applied Sciences, IKGPT University, Kapurthala-144601(Punjab) India
2Department of Physics, GNDU, Shri Amritsar-143006(Punjab) India
3Department of Applied Sciences, DAV Institute of Engg. And Tech.,
Jalandhar-144002(Punjab) India
Corresponding Author: manokamna12333@gmail.com
ABSTRACT
Solid solutions of perovskite La1-xSrxCo0.50Fe0.50O3; {0.1≤ x≤ 0.4} ceramic material have been synthesized by solid-
state route. Diffraction technique XRD has been used for structural analysis and results confirm single phase as well
ascrystalline behavior of the perovskite. The morphology has been investigated by scanning electron microscopy
which undoubtedly indicates a decrease of granule size by Sr2+doping. Archimedes principle used to calculate the
density which is observed to be decreasing with Sr2+ substitution and also isin good agreement with the
microstructure. Thermogravimetric analyzer and dilatometer have been used to study the thermal properties which
indicate a reduction of Co/Fe near 6000C or above consequently generate the oxygen vacancies in the prepared
material and thermal expansion coefficient value decreased with Sr substitution. The impedance, as well as dielectric
properties, has been studied at dissimilar temperatures as well as the frequency which affirm the non-Debye
relaxation nature of the prepared cathode perovskite. The electrical conductivity value has been investigated to be
larger than 100 S/cm, which recommends it to be anappropriate material for the cathode of solid oxide fuel cells.
Keywords: Fuel Cell, Perovskite, Cathode, XRD, TEC, Dielectric Constant
RASĀYAN J. Chem., Vol. 14, No.2, 2021
INTRODUCTION
The exhausts of fossil fuel sources make it a necessity to locate clean and feasible alternative energy
sources. Solid oxide fuel cell (SOFC) is a striking optional energy source due to its reasonable
inexpensiveness and elevated efficiency.1-4Material fabricates SOFCs play a very important role to
achieve such high efficiency and therefore, in the procession of such material perovskite proved its role as
a significant cathode material of SOFCs.5However, few issues limit the usefulness of these materials
which include electrochemical performance as its electrical conductivity decreased with temperature
reduction and nonequality of thermal expansion coefficient with the electrolyte.6-7The introduction of
element P can considerably decrease the resistance of polarization toward ORR.8-9Magnetic insulators
LaFeO3 have antiferromagnetic ordering and with appropriate ion substitution, it is suggested to be the
cathode of SOFCs.10In lanthanum ferrite (LaFeO3), Fe3+ ion has3d5stable electronic configuration and Sr
substituted LaFeO3 cathodes show hopeful performance regarding the stability and power density at
750°C.11-13Due to excellent oxygen diffusivity, La1-xSrxCoO3-δhas a striking electrode activity and shows
marked dissociation ability towards O2 molecules.14But due to the large quantity of Coincrease the
coefficient of thermal expansion (TEC) and consequence may be crack in the electrolyte ordel aminating
the cathode/electrolyte interface.15 To eliminate these issues we decided to substitute Sr2+ at A siteusing
varying content to form the charge inequity and consequently increase conductivity. Another approach is
to balance the unequal charge by the creation of O2 vacancies on substitution of Co at B side with fixed
concentration. Therefore in the present work La1-xSrxCo0.50Fe0.50 O3(0.1≤ x≤ 0.4),solid solutions have been
prepared by solid-state process and samples are characterized for thermal, structural, dielectric as well as
electrical measurements.

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
EXPERIMENTAL
Bulk material of La1-xSrxCo0.50Fe0.50O3, where x varies from 0.1 to 0.4 was prepared by the solid-state
method. Raw powders of SrCO3, La2O3, CoO and Fe2O3(pure 99.9%, Sigma Aldrich) were used in a
stoichiometric ratio to prepare the samples. The mixed powders were milled for 6 hours by using balls of
zirconia oxide and acetone as solvent. Ball milled powder was mixed further thoroughly by using pestle
and agate mortar for 2 hours in wet medium and then sieved using a 70-mesh sieve. Ground prepared
powder was then exposed to calcination conventionally at1200°C temperature for twelve hours. Obtained
calcined powder was further mixed with 2wt % PVA used for proper binding. Pellets of 1mm thickness
and 10 mm diameter were prepared. Prepared pellets were further sinter conventionally at 1400degree
temperature for two hours for proper grain growth and densification of the samples.
RESULTS AND DISCUSSION
Structural Analysis and Physical Properties
X-ray powder diffraction (XRD) of the samples was carried out by x-ray diffractometer from Shimadzu
Maxima 7000 (Japan) at room temperature. X-rays of wavelength (λ) 1.54 Å were used to obtain the
diffraction pattern with a 0.02 degree step size, range 20° to 80° and speed of two degrees/minute. XRD
patterns are given away in Fig.-1. The elevated intensity and pointed crystalline peaks recognized that the
prepared samples were well crystallized. X'Pert High Score Plus software was used to analyze the XRD
data. All the peaks present in XRD patterns were indexed according to crystal structure cubic, Pm-3m
space group and its number is 221. In the XRD pattern, no one crystalline peak left unidentified which
recognized that the solid solution was very fine crystallized in the solo phase. The different parameter
belongs to crystallography are showing in Table-1.
Fig.-1: XRD Patterns of La1-xSrxCo0.50Fe0.50O3(0.1≤ x≤ 0.4) Perovskites
Table1: Crystallographic Parameters of La1-xSrxCo0.50Fe0.50 O3(0.1≤ x≤ 0.4) Perovskites
Composition
Lattice Parameters
Cell Volume
V (Å 3)
Volume
(Occupied)
Volume
(Specific Free)
a =b=c (Å)
La
0.90
Sr
0.10
Co
0.50
Fe
0.50
O
3
3.88
58.411
40.531
0.30611
La
0.80
Sr
0.20
Co
0.50
Fe
0.50
O
3
3.83
56.181
40.759
0.27451
La
0.70
Sr
0.30
Co
0.50
Fe
0.50
O
3
3.78
54.010
40.987
0.24112
La
0.60
Sr
0.40
Co
0.50
Fe
0.50
O
3
3.79
54.439
41.215
0.24291
Microstructure
A scanning electron microscope was used to determine the surface morphology as well as the average grain
size of the prepared perovskite samples. The SEM micrographs of prepared solid solutions are shown in
Fig.-2. The grains are very well attached because of the good sintering of the material. The grains are

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
randomly oriented, non-uniform and the size of the grains is observed to be decreasing with Sr doping at
the A- site of perovskite samples. Values of average grain size are given in Table-2.
Fig.-2: Micrographs of La
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
(0.1≤ x≤ 0.4) Solid Solutions
Density
Archimede’s method was used to determine the density (experimental) of the material. Density
(theoretical) was obtained by using the following equation:
a
l i q u i d
a l
W
W W
 
 

Where W
l
and W
a
are the weight of prepared pellets in fluid and air respectively. ρ and ρ
liquid
is the density
of prepared pellet and density of the used fluid respectively. The density of the material lowered with the
increasing Sr concentration in the material. Density, grain size, and tolerance factor are given in Table-2.
Table-2: Calculated Density, MeanGrainSizeas well asTolerance Factor of La
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
(0.1≤ x≤ 0.4).
Samples
Density
MeanSiz
e of
Grain
(μm)
Deviation
(size)
Tolerance
factor
Density
(d
Theoretical
)
(g cm
-3
)
Density
(d
Experimental
)
(g cm
-3
)
[d
Experimental
/d
Theoretical
]
(%)
La
0.90
Sr
0.10
Co
0.50
Fe
0.50
O
3
5.8782
5.683
96.679
0.54
0.24
0.730
La
0.80
Sr
0.20
Co
0.50
Fe
0.50
O
3
5.71997
5.646
98.706
0.50
0.26
0.731
La
0.70
Sr
0.30
Co
0.50
Fe
0.50
O
3
5.56351
5.544
99.649
0.24
0.21
0.732
La
0.60
Sr
0.40
Co
0.50
Fe
0.50
O
3
5.40878
5.335
98.635
0.19
0.16
0.732
Thermo-gravimetric Analysis
The thermo-gravimetric analysis (TGA) of the sintered pellet was obtained in an air atmosphere at a
heating rate 5 °C per minute with a temperature range of 50 °C to 800 °C with Al
2
O
3
powder were used as
reference material. Thermogravimetric analysis curves ofLa
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
ceramic for x = 0.1 and
0.4are shown in Fig.-3. TGA curves initially show sharp weight loss up to temperature 200°C -300 °C.
This weight loss may occur due to loss of the moisture present in samples as well as carbonate change
into oxides. Above 300 °C the weight change is comparably small. In the perovskite material creation of
oxygen vacancies at high temperatures may be the reason for weight loss. Weight change rose because of
charge imbalance occurs in the prepared material on Sr
2+
substitution at A -site which is compensated by
a reduction of Co/Fe substituted at B -site of the LaFeO
3
perovskite material.
16,17
Thermal Expansion Coefficient
Mismatching of TEC with another component of the cell gives rise to thermal stresses and reduces cell
performance. ΔL/L
0
versus temperature curves for all the compositions of prepared materials up to

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
temperature 800 °C are shown in given Fig.-4. The calculated value of TEC of La1-xSrxCo0.50Fe0.50O3 for
x belongs to 0.1 and 0.4 at temperatures 200 degrees and 800 degrees is 15.4 ×10-6 and 13.7×10-6 per
degree Celsius respectively. The main cause of lowering or raising TEC is gain or loss of lattice oxygen
of the oxides at high value of temperature and also the existence of superstructure in addition to the
ordering of O2 vacancies may be the cause of change in TEC because potential energy well becomes more
symmetric with the high-quality ordering of oxygen vacancies.17-18 In prepared material with Sr doping
the TEC, value is decreased which shows that reduction of Co takes place at a high value of temperature
which gives rise to the formation of O2 vacancies in the solid because of larger radii (ionic) of Co3+ as
compare to Co4+.
Fig.-3: TGA Curves of La1-xSrxCo0.50Fe0.50O3(x = 0.1 and 0.4) Solid Solutions
Fig.-4: Thermal Expansion Curves of La1-xSrxCo0.50Fe0.50O3(x = 0.1 and 0.4) Solid Solutions
Dielectric Properties
Relative dielectric permittivity is the function of frequency, expressed by the subsequent relation:
εr[ω] = ε′ [ω] – iω ε″ [ω]
Where ε′ [ω]be dielectric constant (real component) which is in phase using field applied and ε″[ω] be the
imaginary component of dielectric constant which is in quadrature using field applied. εr= ε/ εo.(εo is the
dielectric permittivity in free space) furthermore, ω be angular frequency. The temperature-based ε′, as
well as ε″ with respect to frequency of applied field at dissimilar temperature values, are shown in Fig.-
5as well asFig.-6, respectively. Both εʹ, as well as ε″ curves, are fitted using the Cole-Cole model given
below which represents a relaxation model inured to express dielectric relaxations.19 Exponent α, be a
parameter that is inured to depict varied spectral shapes. When 𝛼 = 0, the Cole-Cole model represents
Debye behavior and confers stretched relaxation. On the other hand α  0, signifying that systems moving
towards non-Debye nature. Table-3 indicates that the exponents, all α - values above zero signifying the
non-Debye relaxation nature of the system.

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
𝜀′= 𝜀∞+(1 + sin 
(𝜔𝜏)())(𝜀− 𝜀∞)
(1 + (𝜔𝜏)()+ 2 sin 
(𝜔𝜏)())
ε″ = (𝜔𝜏)() cos
)(𝜀− 𝜀∞)
(1 + (𝜔𝜏)()+ 2sin
(𝜔𝜏)())
In the lower region of frequency both ε′ (real)and ε″ (imaginary) incessantly decrease concerning
frequency by the side of all value of temperature and nearly show a linear behavior in the area of elevated
frequency. This kind of behavior is incredibly well described by the dipolar relaxation phenomenon.20 In
the lower frequency region, all forms of the polarizations ionic, electronic, dipolar and space charge
contribute their role and result in the highest polarizability. In the area of elevated frequency both ε′ in
addition to ε″ drop back the switching signal of orientation like dipolar, which further consequences
around linear variation in that region because of filter out few polarizations among the overall
polarizability. This variation perhaps rose due to polarization like interfacial and does not belong to
polarization like dipolar.
Fig.-5: Variation of Real Component ε′ Concerning Frequency of La1-xSrxCo0.50Fe0.50O3(0.1≤ x≤
0.4) Perovskite
Fig.-6: Variation of Imaginary Component ε′′ with respect to Frequency of La1-xSrxCo0.50Fe0.50O3(0.1≤ x ≤ 0.4)
Perovskite

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
Table-3: α–Parameter Values at Dissimilar Temperature of La
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
(0.1 ≤ x ≤ 0.4) Perovskite
Temperature
(˚C)
LSCF
-
0.10
LSCF
-
0.20
LSCF
-
0.30
LSCF
-
0.40
ε

ε

′
ε

ε

′
ε

ε

′
ε

ε

′
60
0.412
0.034
0.391
0.042
0.417
0.045
0.451
0.083
120
0.365
0.028
0.423
0.012
0.366
0.024
0.348
0.097
180
0.85
0.013
0.384
0.094
0.384
0.016
0.376
0.084
240
0.846
0.035
0.412
0.101
0.348
0.023
0.643
0.091
Impedance Spectroscopy
The real component Z′, as well as imaginary component Z″ of impedance w.r.t. frequency for x= 0.10 and
0.40 samples in temperature range 60oC to 240oC, is shown in Fig.-7. From the graph, it is revolved that
Z′ has a large value at the lesser value of temperature moreover also with increasing frequency, its
magnitude decreases which confirm that the prepared material show typical negative temperature
coefficient of resistance.
21
Fig.-7: Variation of Z′ (real) and Z″ (Imaginary) VsFrequencyLa
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
(x = 0.1 and 0.4) Perovskite
Therefore, decreasing the value of Z′ with increasing both frequency and temperature indicates
enhancement of electrical conductivity.
22,23
Z′ merges ina region of high frequency show that material has
a reduction of barrier properties.
24,25
The decreasing character of Z″ with enhancing both frequency and
temperature confirm the fall of the resistive natureof the material. Peaks broadeningon increasing the
temperature revolves that the prepared samples show temperature based electrical relaxation occurrence
and in the region,soaring frequency, merging of Z″ curves indicate the disappearance of polarization
raised doe tospace charge.
26,27
Electrical Properties
The conductivity of the prepared samples has been calculated using formula G


= σac, where G be the
conductance, σac be the ac conductivity, l be thickness and A be the cross-sectional area of the pellets.
Electrical conductivity variation relating to temperature at dissimilar frequencies from 25°C temperature
to 600°C temperature ofLa
1-x
Sr
x
Co
0.50
Fe
0.50
O
3
(x=0.1 and 0.4) samples is exposed in Fig.-8. It is
undoubtedly found from the graph that with enhance in temperature as well as frequency conductivity
continuously increases. The maximum value of the conductivity is 156.44 S/cm as well as 189.80 S/cm
for x=0.1 and 0.4 respectively, which also shows that the Sr modification increases the conductivity.
At a high value of temperature, Co
3+
/ Fe
4+
ions reduce to Co
2+
/(Fe
2+
/ Fe
3+
) ions and result in the
generation of oxygen vacancies in the materials. As the Sr doping has been enhanced in the material,
there may be the extra probability of reduction of ions and creation of O
2
vacancies in the prepared

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
material which future becomes the cause of raising the conductivity of the material. Grain size, grain
boundaries and defects of the material play an especially important part in the conductivity of the
material.
Fig.-8: Variation of Conductivity with respect to Temperature of La1-xSrxCo0.50Fe0.50O3 ;(x = 0.1 and 0.4)Perovskite
Also, alkaline earth metals cations form ordered oxygen vacancies clusters in materials by acting like
nucleating sites which can make them engaged for conduction.28,29 At a low value of temperatures, some
extra energy is required for the dissociation of formed clusters for making the ions mobile. Therefore, the
net activation energy of the material is the sum of dissociation as well as migration energy. On another
side, the energy required at a high value of temperature is only for ions mobility inside the material and
consequently, total activation energy is connected to migration energy which is always less than the value
of activation energy at low temperature.30,3. The activation energy of the material has been obtained by
the Arrhenius fit of electrical conductivity relating to temperature and shown in Fig.-9.
Fig.-9: Arrhenius Curves (ln σ vs. 1000/T) of La1-xSrxCo0.50Fe0.50O3 for (x = 0.1 and 0.4) Solid Solutions
Activation energy value calculated for x=0.10 sample is 0.23 eV and for x=0.40 sample its value is 0.21
eV which also confirm that with Sr substitution, energy value decreases. The activation energy value of
the material is established to be in superior agreement with the results of the obtained value of the
conductivity.
CONCLUSION
La1-xSrxCo0.50Fe0.50O3{0.10≤ x≤ 0.40} perovskite ceramic material has been synthesized via solid-state
method. The XRD confirms the cubic structure and single phase of the material. The obtained
micrographs confirm that mean grain size constantly falls with rising Sr2+ substitution which in excellent
agreement with the density value of the material. TGA graph shows the reduction of the material which
causes the weight loss of the material. TEC value falls with Sr substitution and lies in the range (13.7-
15.4) ×10-6 °C-1for x=0.10 to 0.40.The dielectric constant is large at low frequency and has a low value at

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La1-xSrxCo0.50Fe0.50 O3 {0.1≤ x≤ 0.4} CATHODE FOR SOFCS Manokamna et al.
high frequency. The impedance analysis established the non-Debye relaxation conduct of the samples.
The electrical conductivities at unlike temperatures and frequencies have been increased with increasing
Sr2+ content in the material.
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[RJC-6153/2020]