Structural and electrical properties of double perovskite: (BaSr)FeMoO6

Article abstract of DOI:10.1016/j.physb.2020.412522

In this article, the structural, micro-structural, and temperature-frequency dependence of electrical characteristics of double perovskite (BaSr)FeMoO₆ have been reported. The compound crystalizes in cubic symmetry with lattice parameter a = 7.9280 (2) ?, and V = 245.95 (?)³. The micro-structural study suggests the uniform distribution of grains on its surface with small voids. The obtained high dielectric constant and low tangent loss value may be applicable for capacitor. In the impedance analysis we observed the behaviour of negative as well as positive temperature co-efficient of resistance. The study of the Nyquist plot suggests the existence of only grain effect. Based on both impedance and modulus spectroscopy, dielectric relaxation process is found to be of a non-Debye type. The frequency dependence of conductivity obeys the Jonscher's Power law which suggests the conduction phenomenon follows the non-overlaping small polaron tunnelling and correlated barrier hopping models. The calculated activation energy in the conduction process may be used in electron hoping. The comparative study of Z?? and M?? with frequency suggests the existence of short range ordering of charge carriers. The leakage current study reveals that the conduction mechanism follows the space charge limited conduction phenomenon.

Full text of DOI:10.1016/j.physb.2020.412522

Journal Pre-proof
Structural and electrical properties of double perovskite: (BaSr)FeMoO
Rutuparna Das, R.N.P. Choudhary
6
PII:
S0921-4526(20)30522-6
DOI:
https://doi.org/10.1016/j.physb.2020.412522
PHYSB 412522
Reference:
To appear in: Physica B: Physics of Condensed Matter
Received Date: 27 May 2020
Revised Date: 29 August 2020
Accepted Date: 30 August 2020
Please cite this article as: R. Das, R.N.P. Choudhary, Structural and electrical properties of
double perovskite: (BaSr)FeMoO , Physica B: Physics of Condensed Matter (2020), doi: https://
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Credit Authors Statement
•
The corresponding author is responsible for ensuring that the descriptions are
accurate and agreed by all authors.
•
Rutuparna Das: Synthesis of sample, structural and electrical characterization,
prepared the manuscript, R N P Choudhary: Some analysis in the paper and
supervise the work.

Structural and Electrical Properties of Double Perovskite:
(BaSr)FeMoO6
*Rutuparna Das, R N P Choudhary
Department of Physics, Siksha O Anusandhan (Deemed to be University)
Bhubaneswar-751030, Odisha, INDIA
*Corresponding author:rutulucy2013@gmail.com
Abstract:
In this article, the structural, micro-structural, and temperature-frequency dependence of
electrical characteristics of double perovskite (BaSr)FeMoO6 have been reported. The
compound crystalizes in cubic symmetry with lattice parameter a=7.9280 (2) Å, and
V=245.95 (Å)3. The micro-structural study suggests the uniform distribution of grains on its
surface with small voids. The obtained high dielectric constant and low tangent loss value
may be applicable for capacitor. In the impedance analysis we observed the behaviour of
negative as well as positive temperature co-efficient of resistance. The study of the Nyquist
plot suggests the existence of only grain effect. Based on both impedance and modulus
spectroscopy, dielectric relaxation process is found to be of a non-Debye type. The frequency
dependence of conductivity obeys the Jonscher’s Power law which suggests the conduction
phenomenon follows the non-overlaping small polaron tunnelling and correlated barrier
hopping models. The calculated activation energy in the conduction process may be used in
electron hoping. The comparative study of Zʹʹ and Mʹʹ with frequency suggests the existence
of short range ordering of charge carriers. The leakage current study reveals that the
conduction mechanism follows the space charge limited conduction phenomenon.
1

Key words: Double perovskite; X-ray diffraction; Nyquist plot; Jonscher’s power law; Space
charge limited conduction; Complex impedance study
1. Introduction:
Now-a-days, there has been growing demand for searching of room temperature magneto-
electric multiferroic materials for both fundamental scientific understanding and to develop
the novel multifunctional devices. Multiferroics are the materials in which at least two of the
three ferroic properties, namely ferroelectricity, ferromagnetism and ferroelasticity, coexist.
Due to the coupling between ferroelectric and magnetic domains, the multiferroic materials
offer a novel class of applications in multistage information storage devices, like FeRAM,
MRAM etc.[1-2]. Spintronics is a field of investigation for developing the influence of
electron spin on the electrical conduction. Spintronic materials possess the unique
possibilities for use in new functional microelectronic devices, ideal memory media for
computing and in the direction of quantum computing due to its advancement in nonvolatility
and magnetic random access memory (MRAM). This technology could also be used to create
electronic devices, which should be smaller, faster and consume less power. Hence, the half-
metallic elements with high spin polarization can enhance device performance, and are
necessary for a new generation of spintronic devices. There is more attention for the
discovery of new perovskite materials having high Tc half-metals. The perovskites (ABO3) or
multiple perovskites belong to a large class of oxide materials have wide industrial
applications. The family of double perovskites first received attention in the 1960s [3]. The
double perovskite (DP) materials with a general chemical formula (AA')(BB')O6 are the
combinations of two perovskites: ABO3 and A'B'O3. In (AA')(BB')O6, A and A' correspond
to alkaline or rare earth cations, whereas B and B' are transition metal cations. If A and A' are
the similar elements, then the compound has the formula A2(BB')O6. Such type of materials
exhibit wide characteristics, such as semiconducting, conducting, half-metallic, insulating,
2

ferroelectric, thermoelectric, and superconducting [4-5].They display interesting magnetic
and electronic characteristics with half metallic and low field magneto-resistance. The
electric and magnetic properties of the materials are interconnected because of the same (d)
character of the “conduction” and “magnetic” electrons. The exchange interaction may
happen between ions of the same element along with ions of different elements. The
interaction among charge, spin, and lattice results in various electronic and magnetic
characteristics, like metallic ferro- or ferri-magnetism or anti-ferromagnetic or paramagnetic
insulating property. This also brings about the magneto-resistive properties of the
compounds. The electronic and magnetic properties in the double perovskite system can be
controlled by substitution of alkaline earth metals (e.g. Ba, Sr, Ca) or lanthanides (e.g. La, Pr,
Nd) at the A-site, as well as by the substitution of transition metals (e.g. Fe, Cr, Mn, Mo, Rh,
Ru, W, Re). The discovery of low-field magneto-resistance (LFMR) and half-metallic
property of the Sr2FeMoO6 (SFMO) compound were investigated by Kobayashi et al. [6]. A
fully spin polarized half metal, SFMO exhibits a high Curie temperature (>400 K) and
excellent magneto-resistance response at relatively small applied fields, and at high
temperatures compared to manganites, making it an ideal candidate for room temperature
spintronic applications. The magneto-resistive (MR) properties in double perovskite SFMO
generally arise from spin-dependent scattering at the grain boundaries. In the double
perovskite crystal structure, the oxygen and the large transition metal cations are closely
packed, whereas B and Bʹ are arranged inside the oxygen octahedra. The position of the B
and Bʹ octahedral is alternating for B and Bʹ elements with a large difference of ionic radii. In
the case of a small difference in B and Bʹ ionic radii, a random arrangement of B and Bʹ
occurs. The arrangement of the B and Bʹ octahedral influences the B–O– Bʹ, B–O–B, or Bʹ –
O– Bʹ exchange interactions, and therefore, it is very important for understanding the
structural, magnetic, and electronic properties of such type of compounds. The low field
3

magneto-resistance of such type of compounds is connected to the half-metallic nature of
their ground state. The half-metallic nature and the high degree of spin polarization of the
charge carriers are also very important for the technical applications of the DP [7-9]. Because
of above discussed factors, double perovskite can display a variety of crystal structures for
different alkaline and transition metal ions [10-11]. The room temperature structure can be
cubic for Sr2FeMoO6 [12], Ba2FeMoO6 [13]; tetragonal with I4/mmm symmetry, as observed
in the case of Sr2FeMoO6 [14]; and monoclinic with P21/n or P21/c: Ca2FeMoO6 [13]. The
differences between the structures of the same compound, e.g. Sr2FeMoO6, can be associated
with difference in the chemical composition of DP fabricated under different conditions. As a
result, there are some differences in the oxygen stoichiometry along with B, Bʹ ions ordering,
and structural defects produced. It is worth noting that when A2 = Ba2 and SrBa, the
compounds crystallize in the cubic structure [15]. Most of the double perovskites have been
discussed which show good conducting at a high temperatures with electro-catalytic nature.
Sr2FeTiO6 is one of the multiferroic double perovskite compounds which are appropriate for
sensors and actuators purpose [16]. SFMO (Sr2FeMoO6) is a typical double-perovskite
(ordered) structure, having an alternating regular arrangement of FeO6 and MoO6 in a rock
salt super-lattice, where Sr cations make the voids between the octahedral. The radius and
charge differences among Fe3+ and Mo5+ are 0.035 and 2 respectively; making fractions of
Fe3+ and Mo5+ reside at the B and B' sites arbitrarily. There is also a fraction of Fe atoms
acquiring the B' site, and an equivalent of Mo atoms occupies at the B site which is called the
antisite (AS) defect. SFMO has a high Curie temperature (410–450 K) and low-field room-
temperature magneto-resistance. This material may be applicable for magnetic sensors and
spintronics owing to its large spin-polarization [17-19]. The properties of double perovskite
materials mostly depend on the B-site cations arrangement, which modifies the structural
phase transition, electrical and magnetic characteristics. The ordering arrangement can be
4

controlled by various factors, like the A/B size ratio and oxidation states in the double
perovskite materials. For example, dominating characteristics of anti-ferromagnetism of
Sr2LnMoO6 and ferri-magnetism of CaLaMnMoO6 has been reported. It is noted that two
dissimilar cations at the B-site of double perovskite may permit the two different types of
magnetic sub-lattices (a magnetic and a non-magnetic sub-lattice). For instance, the
relationship between magnetic 3d cations with non-magnetic 4d or 5d ions leading to ferri-
magnetic metallic ordering in Sr2FeMoO6, Sr2CrWO6, and Sr2CrReO6 [20]. From the detailed
literature survey on the above double perovskites, it is found that the Fe–Mo containing
compounds have recently attracted a great deal of interest of researchers because of their
many interesting properties useful for applications. As compared to the manganese based
double perovskites, the Fe-Mo materials possess high magnetic ordering temperature which
make them suitable for magneto-electronics or spintronic applications. Based on their results
and knowing the importance of these compounds, attempt has been made to tailor the
physical properties of Sr2FeMoO6 by modifying its A-site to get (BaSr)FeMoO6 compound.
Apart from that, some evidences about the magnetic characteristics of such compounds have
only been discussed before. Knowing the importance of materials for applications, some
interesting work has been reported recently. As the detailed studies of structural and electric
characteristics of such material have not been analysed, we have carried out the same
(structural, micro-structural, dielectric, and electrical characteristics) of (BaSr) FeMoO6
which is presented in this paper.
2. Experimental Technique:
The double perovskite ceramic material (BaSr)FeMoO6 was prepared via a standard ceramic
technology solid-state reaction method using high-purity (>99.9%) or AR grade) ingredients,
such as strontium carbonate SrCO3 (M/S Loba Chemie Co Pvt Ltd), barium carbonate BaCO3
5

(M/S Central Drug House), iron carbonate FeCO3 (M/S Central Drug House), molybdenum
trioxide MoO3 (M/S Central Drug House) in stoichiometry. These ingredients were mixed
thoroughly in agate mortar and pestle by both dry and wet grinding modes. Then the powder
was calcined at 11500C in an alumina crucible. The phase formation was confirmed from the
analysis of X-ray diffraction collected by the X-ray diffractometer (Rigaku Ultima-IV) in a
wide range of Bragg angle (20° ≤ 2θ ≤ 80°) with a scanning rate of 2°/min. and CuKα
radiation of wavelength 1.5416 Å. The cylindrical pellets were made by adding polyvinyl
alcohol with calcined powder using KBr hydraulic press. The pellets were sintered at 1200oC
at atmospheric pressure for 4 h. The room temperature surface morphological study of the
sintered pellet was carried out with a scanning electron microscope (SEM, ZEISS). The
elemental analysis of the compound was done by studying the energy dispersive analysis of
X-ray (EDAX) spectrum. To obtain a smooth surface, two sides of the pellet were polished
and coated with high-purity silver paste followed by heating treatment to make moisture-free.
By using an impedance analyzer (N4L PSM, 1735), all the electrical parameters were
obtained in the frequency range of (1kHz–1MHz) at different temperatures (25–300°C). The
leakage current characteristic data of the studied material were obtained using Keithley
electrometer (model 6517B).
3. Analysis of results:
3.1 Structural and microstructural analysis:
Fig.1 (a) displays the XRD pattern (room temperature) of (BaSr)FeMoO6. All the peaks of
the X-ray pattern are analysed with the software “Expert Highscore plus”. The XRD pattern
of this compound consists of cubic (BaSr)FeMoO6 (ICSD: 01-070-4084) and tetragonal
Ba(MoO4) (ICSD: 01-089-4570). The cell parameters were obtained and refined using
standard software “POWD MULT” which are: a=7.9280 (2) Å, and V=245.95 (Å)3 (figure in
parenthesis implies the observed standard deviation). The crystallite size (D) of the
6

compound was determined by the Scherrer’s equation [21-22]. The magnitude of D is
obtained to be 42 nm. Fig.1 (b) displays the room temperature scanning electron microscope
of a pellet sample. The grains of different sizes are uniformly (almost) distributed over the
surface describing the polycrystalline character of the material. The EDAX pattern (Fig.1(c))
represents a compositional study that shows the existence of essential elements (Ba, Sr, Fe,
Mo, O) without any foreign particle. Fig.1 (d) represents the elemental mapping of
(BaSr)FeMoO6 compound.
7

(c)
8

(d)
Fig.1: (a) X-ray diffraction pattern, (b) SEM, (c) EDAX and (d) elemental mapping of
(BaSr)FeMoO6
3.2 Dielectric Property
:
For a ceramic material, the dielectric characteristic is one of the most important properties.
Such analysis yields significant information regarding the defects, the quantity of polarization
and source of dielectric loss, etc. The dielectric constant of the compound was determined by
ꢂꢃ
ꢅ
the relative relation ꢀꢁ=
Where Cp = parallel capacitance (obtained experimentally), C0
ꢂꢄ
= absolute permittivity [23].
9

3.2.1 Frequency dependence of dielectric property:
Fig. 2: Plot of (a) εr and (b) tanꢆ with frequency of (BaSr)FeMoO6
Fig. 2(a-b) is depicted as the frequency dependence of dielectric constant and tanꢇ. We
observed the systematic and smooth variation of these parameters with temperature and
frequency. Since both these parameters reduce with the increment of frequency and
temperature, the material behaves like a normal dielectric material. Such a trend in the
dielectric spectrum may be ascribed to the various type of polarization (electronic, ionic,
dipolar, and space charge polarization). All these polarizations follow the time-varying
change electric field in the low-frequency region. Therefore, in such a region, the dielectric
constant value is high. All the dipoles may not follow the changing field with an increment of
frequency. Thus, the different polarizations are filtered out with an increment of frequency
results decrement of dielectric constant [24]. The dielectric dispersion can well be understood
by the Koop’s phenomenological and Maxwell–Wagner theory [25-26]. According to this
theory, the dielectric medium is made up of grains (more conducting) and grain boundaries
(less conducting). The grains and grain boundaries are highly sensitive at high and low
10

frequency respectively. The decrement of ꢀr with the enhancement of frequency may be the
main cause of hopping of electron at octahedral sites that lags behind the changing electric
field. Therefore, electrons pass through both the grains and grain boundaries. Since the grain
boundaries are low conducting, the electrons are accumulated near it and develop more space
charge polarization. Hence, ꢀr value increases in the low-frequency sides. When frequency
increases more and more, the electrons suddenly alternate their path, making obstacles for the
motion of electrons in the materials, thereby reducing the gathering of electrons and also ꢀr.
In Fig. 2(b), the dielectric loss shows the similar trend as of dielectric constant. The low-
frequency tanꢇ increases significantly with the rise of temperature representing the part of the
dc conductivity owing to the hopping of electrons.
3.2.2 Temperature dependence of dielectric permittivity:
The temperature response of ꢀr and tanꢇ for BSFMO are represented in Fig. 3(a-b). The
d
ielectric constant rises gradually with increasing temperature. Such an increasing trend of
the dielectric constant with the enhancement of temperature corresponds to the interaction of
electron and phonon [27].
11

Fig. 3: Temperature dependence of (a) εr and (b) tanꢆ of (BaSr)FeMoO6
In Fig.3 (a), it is noticed that the room temperature magnitude of εr at 1 kHz is nearly equal to
2000, and the value increases with an increase in temperature. Fig. 3(b) displays the variation
of temperature dependence of tanδ of the studied material. It is observed that at low-
temperatures, the magnitude of tanδ is low, but the tanδ value rises with the enhancement of
temperature. This happens because of thermally induced charge carriers and defects. A broad
dielectric loss peak is observed corresponding to the quick drop of the dielectric constant.
The loss peak shifts to the high temperature side as the frequency increases, suggesting the
thermally stimulated dielectric relaxation in the present ceramics. For a pure system, the
compound should have a low dielectric loss and high resistance. During calcination and
sintering, the charge carriers (electrons) and oxygen vacancies are produced. There may be
the chance of the creation of a single/doubly ionized oxygen vacancy with the liberation of
one or two electrons from the oxygen. By Kröeger–Vink notation, we have the following
equations:
12

ꢊ
ꢈꢉ = ꢈꢋ + ꢌ ꢍ + ꢎꢏ……………………………………………………………………… (1)
ꢉ
ꢋ
ꢊ
ꢈꢉ = ꢈꢋ + ꢌ ꢍꢍ + 2ꢎꢏ…………………………………………………………………… (2)
ꢉ
ꢋ
In this situation, the dipole can be formed by the combination of the ion with a single ionized
oxygen vacancy. The dielectric relaxation is affected by these dipoles. The oxygen vacancy is
not confined only in the unit cell, but it can affect the total system resulting in the rise of ionic
conductivity [28-29]. The stepwise reduction in dielectric constant involves distinct
transition, resembles the respective peaks in dielectric loss with the peak positions moves to
higher temperatures as frequency raises. This demonstrates the existence of thermally
activated relaxation in the material.
3.3 Impedance Analysis:
The complex impedance spectroscopy is usually used to study the electrical characteristics of
the materials. The frequency (ω) dependent impedance data are usually analysed in terms of
the real and imaginary components of complex impedance (Z), modulus (M), admittance (Y),
and permittivity (ε). The impedance of the circuit Z(ω) at an applied frequency ω (angular
frequency) can be expressed in both polar as well as Cartesian form as below.
Z (ω) = ׀Z׀ exp (-jθ) = ׀Z׀cosθ - j׀Z׀sinθ = Z΄ - jZ˝ ………………………………….. (3)
Where, Z΄ and Z˝ are the real and imaginary part of the complex impedance (Z) respectively.
For a parallel combination of R (resistance) and C (capacitance) in a circuit, the complex
impedance Z (ω) can be expressed by
ꢘ
ꢘ
ꢘ
ꢊ
ꢖꢏꢐꢑꢗꢖ
ꢖ
ꢑꢖ ꢗ
Z(ω) = ꢐꢑꢒꢓ
=
= [ꢊꢓ(ꢑꢖꢗ)ꢘ] - j[ꢊꢓ(ꢑꢗꢖ)ꢘ]……………………………………..(4)
ꢔ
ꢕ
ꢊꢓ(ꢑꢗꢖ)
13

After solving the equation, the real and imaginary part of Z (ω) will be written as
ꢘ
ꢖ
ꢑꢖ ꢗ
Z΄ = ꢊꢓ(ꢑꢖꢗ) and Z˝ = ꢊꢓ(ꢑꢗꢖ)
…………………………………………………… (5)
ꢘ
ꢘ
Admittance: Y = (Z∗)−1…………………………………………………………………(6)
ꢊ
Complex modulus M = ꢙ∗ = M' + jM''……………………………………………… …… (7)
Complex permittivity ꢀ∗= ꢀ′- jꢀ′′…………………………………………………………. (8)
Fig.4: Plot of (a) Z' and (b) Z'' with frequency at different temperature of
(BaSr)FeMoO6
Where ꢚ=angular frequency, R= resistance of the material, and relaxation time is determined
by using a relation ꢛ = ꢜꢝꢂꢝ (Cg, Rg are the effective capacitance and resistance in parallel).
Fig.4 (a) and (b) represents the curve of frequency dependence Z' and Z'' respectively. The Z'
value decreases at low-frequencies, whereas all the Z' curves merge at a high frequencies. It
is indicated that the low-frequency Z' value is temperature-dependent. The reduction of Z'
value with the enhancement of temperature (up to 225) indicates the semiconductor type of
14

behaviour (ie., (negative temperature coefficient of resistance or NTCR)) at high
temperatures, whereas for 2750C the magnitude of Z' rises with an increment of temperature
correspond to PTCR (positive temperature coefficient of resistance) behaviour of the
material. The coinciding of high-frequencies Z' value suggests the liberation of space charges
leading to the decrease in the activation barrier of the material with a rise in temperature [30-
31]. In Fig. 4(b), the magnitude of zʹʹ increases gradually up to a certain frequency. The peak
position of the zʹʹ moves in the high-frequency region with the rising of temperature
indicating the occurrence of relaxation phenomenon in the compound. The width of the peak
determines the distribution of relaxation time. The most probable relaxation time is given by
τm (=1/ωm). The unsymmetrical widening of the peaks demonstrates the occurrence of the
electrical process of the sample with a spreading of relaxation times as determined by the
peak width [32].
Fig.5: Nyquist Plot of Z' with Z'' (a) at 25-2750C, (b) 250C with the depression angle of
(BaSr)FeMoO6
15

3.4 Nyquist plot:
Fig.5 (a) depicts the Nyquist plots which show correlation between real and imaginary parts
of complex impedance. The complex impedance of the materials may be demonstrated by
ideal equivalent circuits having resistors R and capacitors C to study the electrical
characteristics of the material. The association of the RC network with the constant phase
element (Q) indicates the deviation from the Debye-type nature [33-34]. In such a technique,
the impedance spectrum is symbolized by semicircular arcs. In this method, the test and
theoretical data were verified by (ZSIMP WIN version 2.0) software [35].In the present case,
we found a single semicircle (RQC) signifying the occurrence of only grain effect. Apart
from that, the depressed semicircular arcs with certain angles (Fig.5 (b)) which centres
situated below the real axis corresponding to the non-Debye type of relaxation.
3.5 Analysis of conductivity:
Fig. 6(a) represents the frequency versus ac conductivity curve at various temperatures. This
plot consists of a frequency-independent plateau area (dc conductivity) and frequency
dispersion region (ac conductivity). The ac conductivity remains frequency-independent up to
100 kHz then the conductivity rises with the enhancement of frequency. The increase of
conductivity with the enhancement of temperature may be accredited to free as well as a
bound charge from different regions (grain and grain boundaries) in ceramics that are
scattered in-homogeneously. This leads to a change in activation energy with temperature
[36].To describe the frequency dispersion of the conductivity spectra, the conductivity data
can be demonstrated form Jonschor’s universal power law [37]
ꢞꢟꢒ= ꢞꢠꢒ + Aꢚꢡ…………………………………………………………………………..(9)
16

Where ꢞdc and ꢞac are the dc and ac conductivities respectively. The exponent (n) lies in the
limit of 0 and 1. The value of n = 1 corresponds to pure Debye case. Fig.6 (b) represents the
variation of A and n as a function of temperature. From the curve, it is found that first the
value of A increases and then decreases. The behaviour of the exponent factor n as a function
of temperature can be used to determine the origin of the conduction mechanism. In CBH
(correlated barrier hopping), n reduces with the increase of temperature, whereas, in OLPT
(overlapping large polaron tunneling) model, n decreases first, and then increases with the
increase of temperature, and in small polaron conduction process, n increases with increase in
temperature. In QMT (quantum mechanical tunneling) mode, the magnitude of n ~ 0.8 and is
independent of temperature [38]. In the non-overlapping small polaron tunneling (NSPT)
conduction mechanism, the exponent n increases with increasing temperature [39]. Since the
magnitude of n increases first, and then decreases, the above discussion of the existence
conduction phenomenon belongs to both non-overlapping small polaron conduction (first
increasing part) and CBH model (second decreasing part).
17

Fig. 6: Variation of (a) ꢢac with frequency, (b) A and n with temperature and (c)
ꢢac with 1000/T for (BaSr)FeMoO6
Table 1: The obtained values of n and A of (BaSr)FeMoO6
Temperature (°C)
A
n
25
75
1.3078E-7
8.0395E-6
0.00013
0.0001
0.00953
0.00943
0.01397
0.02166
0.02172
0.02093
125
175
225
275
0.00002
3.3267E-6
Fig.6 (c) represents the variation of ac conductivity with 1000/T of the studied material.
Using the dielectric data, ꢞꢟꢒ can be determined by the relation:
ꢞꢟꢒ = ꢚꢀꢁꢀꢄꢣꢤꢥꢇ……………………………………………………………………… (10)
Where ε0 = absolute permittivity. The activation energy can be determined by the expression
[40]:
18

−ꢧ
ꢞꢟꢒ = ꢞꢄexpꢦ ꢟꢫ
ꢨꢩꢪ
ꢬ…………………………………………………………………(11)
Where kB = Boltzmann constant and σ0 = pre-exponential factor. The ac conductivity of the
material increases with the rising temperature that may be the cause of carrier mobility for
hopping, which is enhanced by increasing temperature. This behaviour indicates the
semiconducting type of material. The values of determining Ea are 0.68, 0.77, 0.79, 0.92,
0.95, 0.91 eV at 1, 5, 10, 100, 500 and 1000 kHz respectively. The merging of high
temperature curves suggests the liberation of space charge.
3.6 Modulus Study:
The dynamical nature of the sample can be studied using the complex modulus method. One
of the benefits of the modulus formalism is that it significantly suppresses the electrode
polarization effects [41]. The advantage of representing the dielectric permittivity data in
modulus formalism is that, at lower frequencies, the dominating electrode polarization effects
(on dielectric permittivity) are significantly suppressed, and the generally small capacitance
values of the grains are enhanced [42]. The frequency variation of the real part of the electric
modulus (Mʹ) of the studied material is displayed in Fig. 7(a). It is observed that in the low-
frequency region, the magnitude of Mʹ tends to zero representing the negligible effect of the
electrode, and the Mʹ enhances with the enhancement of frequency. The dispersion of the Mʹ
curves with the enhancement of frequency may be the result of the conduction process due to
the short-range mobility of charge carriers [43].
19

Fig.7: Plots of (a) M' and (b) M'' with frequency and (c) M' with M'' and (d) relative
analysis curve of M″ and Z″ with frequency of (BaSr)FeMoO6
The curves of Mʹʹ with frequency are depicted in Fig.7 (b). The magnitude of Mʹʹ rises with
the enhancement of frequency, and it exhibits a peak in the high-frequency region. The
displacement of M''max peak towards the high-frequency with the enhancement of temperature
resembles that the appearance of relaxation processes in the sample. Unsymmetrical widening
of the peak suggests the spreading of relaxation with the dissimilar time constant [44].The
20

Fig. 7 (c) is represented as the variation of the complex modulus spectrum (Mʹ vs. M'') of the
material. The appearance of a single arc in the spectrum suggests the grain effect in the
compounds [45]. Fig. 7 (d) represents a comparative analysis of impedance (Z'') and modulus
(M″). The matching of Z'' and M″ peaks resemble the long-range ordering of charge carrier
while the mismatching of the peak demonstrates the short-range ordering. In the current
study, we observed that mismatching of the peak which suggests the short-range ordering of
carrier [46].
3.7: Leakage current characteristics:
Fig. 8(a) Leakage current density (logJ–E) and (b) logJ–logE curve as a function of
applied electric fields.
Fig.8 (a) represents temperature variation of current density with electric field (J-E)
characteristics of the studied material for both negative and positive bias. The leakage current
density was lower than 10-3 A/cm2 in the presence of +ve and –ve applied of the electric field
of 400V/cm which is quite reasonable. There are four mechanisms: Schottky emission (SE),
space charge limited conduction (SCLC) mechanisms, modified Schottky– Simmons model,
21

and bulk-limited Poole–Frenkel (PF) ) to understand the conduction process and also to
describe carrier transport in ceramics. To know the existence conduction process, the
observed J–E data was fitted for quantitative analysis of the charge carrier. First, we have
analysed the data for the SCLC mechanism in which the charge carriers are dominated by
space charges. The expression for the current density in SCLC is given by [47-48]
ꢘ
ꢰꢱꢙ ꢙ ꢴꢵ
ꢲ
ꢳ
ꢭꢮꢗꢯꢗ
=
…………………………………………………………… (12)
ꢶꢠ
Where, E is the electric field, ꢀꢁ is the dielectric constant, ꢀꢄ absolute permittivity, ꢷ is the
mobility of carrier, ꢸ is the fraction of injected charge carriers (in trap free limit ꢸ =1). To get
information about the conduction process, we have plotted the graph (Fig.8(b) ) between logJ
and logE. As the obtained slope lies between1-2 so it corresponds to the SCLC mechanism
[49-51].
4. Conclusion:
The polycrystalline material (BaSr)FeMoO6 was successfully prepared by a high-temperature
mixed oxide reaction method. The structural study of the material has been carried out by
XRD analysis, and the compound is found to be in the cubic system with lattice parameter
a=7.9280 (2) Å, and V=245.95 (Å)3. The almost uniform distribution of grains with minor
voids is detected by SEM analysis. The EDAX spectrum suggests the existence of the
necessary element in the compound without any impurity. The frequency dependence of
dielectric study has been explained by the Maxwell-Wagner theory. In the temperature-
dependent dielectric characteristics, we have not found any dielectric anomaly. As the room
temperature dielectric constant and tangent loss are equal to 2000 and 25 respectively at 1
kHz, the material may be useful for capacitor application. In impedance analysis, both NTCR
and PTCR properties of the compound are found. Hence, at low temperatures, this material
22

may be suitable for semiconductor devices. The frequency variation of conductivity was
examined by Jonscher’s power law which reveals that the conduction process follows the
non-overlapping small polaron tunneling (NSPT) and CBH model. The calculated activation
energy in the conduction process may be useful for hopping of electron process. The non-
Debye type of relaxation was found from both impedance and modulus study. The occurrence
of M″ and Z″ peaks at different frequency represents short-range ordering. From J-E
characteristics, the low value of leakage current density was observed and the conduction
mechanism is found to be (SCLC) space charge limited conduction phenomena.
REFERENCE:
[1] S. T. Dadami, S. Matteppanavar, S. I, S. Rayaprol, B. Angadi, B. Sahoo, Investigation on
Structural, Mössbauer and Ferroelectric Properties of (1-x) PbFe 0.5Nb
O3 – (x) BiFeO3
0.5
Solid Solution, Journal of Magnetism and Magnetic Materials 418, 122 (2016)
[2] S. Matteppanavar, S. Rayaprol, B. Angadi, B. Sahoo, Composition Dependent Room
Temperature Structure, Electric and Magnetic Properties in Magnetoelectric Pb(Fe1/2 Nb1/2)O3
- Pb(Fe 2/3W 1/3)O3 Solid-solutions 677, 27 (2016)
[3] N. Kumar, G. Khurana, R. S. Katiyar, A. Gaur, R. K. Kotnala, Double Perovskite
Sr2FeMoO6: A Potential Candidate for Room Temperature Magnetoresistance Device
Applications, doi.org/10.5772/intechopen.70193
[4] C. L. Yuan, S. G. Wang, W. H. Song, T. Yu, J. M. Dai, S. L. Ye, Y. P. Sun, Enhanced
intergrain tunneling magnetoresistance in double perovskite Sr2FeMoO6 polycrystals with
nanometer-scale particles, Appl. Phys. Lett. 75, 3853 (1999)
23

[5] Y. Tomioka, T. Okuda, Y. Okimoto, R. Kumai, K. I. Kobayashi, Magnetic and electronic
properties of a single crystal of ordered double perovskite Sr2FeMoO6,Phys. Rev. B 61, 422
(2000)
[6] K. I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, Y. Tokura, Room-temperature
magneto-resistance in an oxide material with an ordered double-perovskite structure. Nature.
395, 677(1998)
[7] J. Blasco, C. Ritter, L. Morellon, P. A. Algarabel, J.M. De Teresa, D. Serrate, J. Garcia,
M.R. Ibarra, Structural and magnetic details of 3d-element doped Sr2Fe0.75T0.25MoO6
Solid State Sci. 4, 651 (2002)
[8] Y. Moritomo, Sh. Xu, A. Machida, T. Akimoto, E. Nishibori, M Takata, M. Sakata,
Electronic structure of double-perovskite transition-metal oxides, Phys. Rev. B 61, R7827
(2000)
[9] D. Zaja, M. Sikora, V. Prochazka, M. Borowieca, J. Ste¸pien, Cz. Kapusta, P. C. Riedi, C.
Marquina, J. M. De Teresa, M. R. Ibarrac, Local Magnetic and Electronic Properties of the
A2FeMʹO6 (A = Ba, Sr, Ca, Mʹ = Mo, Re) Double Perovskites, Acta Physica Polonica A
111,797 (2007)
[10] F. S. Galasso, F. C. Douglas, R. J. Kasper, Relationship Between Magnetic Curie Points
and Cell Sizes of Solid Solutions with the Ordered Perovskite Structure, J. Chem. Phys. 44,
1672 (1966)
[11] N. Auth, G. Jakob, W. Westerburg, C. Ritter, I. Bonn, C. Felser, W. Tremel, Crystal
structure and magnetism of the double perovskites A2FeReO6 (A=Ca, Sr, Ba),J. Magn. Magn.
Mater. 272, 607 (2004)
24

[12]Y. Moritomo, Sh. Xu, A. Machida, T. Akimoto, E. Nishibori, M. Takata, M. Sakata,
Electronic structure of double-perovskite transition-metal oxides, Phys. Rev. B 61, R7827
(2000)
[13] R. P. Borges, R. M. Thomas, C. Cullinan, R. Suryanarayanan, L. Ben-Dor, L. Pinsard-
Gaudart, A. Revcolevschi, Magnetic properties of the double perovskites A2FeMoO6; A =
Ca, Sr, Ba,J. Phys. Condens. Matter 11, L445 (1999)
[14] J. Navarro, C. Frontera, L. l. Balcells, B. Martinez, J. Fontcuberta, Raising the Curie
temperature in Sr2FeMoO6 double perovskites by electron doping, Phys. Rev. B 64, 092411
(2001)
[15] C. Ritter, M. R. Ibarra, L. Morellon, J. Blasco, J. Garcia, J.M. De Teresa, Structural
and magnetic properties of double perovskites AA'FeMoO6 (AA' = Ba2, BaSr, Sr2 and Ca2)
J. Phys., Condens. Matter. 12, 8295 (2000)
[16] N. Masta, D. Triyonoa, H. Laysandra, Electrical Properties Sr2FeTiO6 Double Perovskite
Material Synthesized by Sol-gel Method, AIP Conf. Proc. 1862, 030036 (2017)
[17] K. I. Kobayashi, T. Kimura, H. Sawada, K. Terakura , Y. Tokura, Room-temperature
magnetoresistance in an oxide material with an ordered double-perovskite structure, Nature
395, 677 ( 1998)
[18] T. H. Kim, M. Uehara, S.W. Cheong , S. Lee, Large room-temperature intergrain
magnetoresistance in double perovskite SrFe1−x(MoꢀorꢀRe)xO3, Appl. Phys. Lett. 74, 1737
(1999)
[19] J. L. MacManus-Driscoll, A. Sharma, Y. Bugoslavsky, W. Branford, L. F. Cohen, M
Wei, Reversible Low Field Magnetoresistance in Sr2Fe2–x Mox O6–δ by Oxygen Cycling and
the Role of Excess Mo (x ꢁ>ꢁ1) in Grain Boundary Regions, Adv. Mater. 18, 900 (2006)
25

[20] S. B. Karki, F. Ramezanipour, Magnetic and electrical properties of BaSrMMoO6 (M =
Mn, Fe, Co, and Ni), Materials Today Chemistry 13, 25 (2019)
[21] N. Pradhani, P. K. Mahapatra, R. N. P. Choudhary, Effect of cerium oxide addition on
optical, electrical and dielectric characteristics of (Bi0.5Na0.5)TiO3 ceramics, J.Phys.: Mater
1, 015007 (2018)
[22] V. Purohit, R. Padhee, R. N. P. Choudhary, Dielectric and Impedance Spectroscopy of
Bi (Ca0.5 Ti0.5) O3 Ceramic Ceramics International. 44, 3993 (2018)
[23] N. Kumar, A. Shukla, R. N. P. Choudhary, Structural, Electrical and Magnetic Properties
of (Cd, Ti) Modified BiFeO3 Physics Letters A 16, 31844 (2017)
[24] ] D. K. Pradhan, R. N. P. Choudhary, C. Rinaldi, R. S. Katiyar, Effect of Mn substitution
on electrical and magnetic properties of Bi0.9La0.1FeO3, J. Appl. Phys. 106,024102(2009)
[25] K. Parida, S. K. Dehury, R. N. P. Choudhary, Structural, electrical and magneto-electric
characteristics of complex multiferroic perovskite Bi0.5Pb0.5Fe0.5Ce0.5O3, Journal of
Materials Science Materials in Electronics 27, 11211 (2016)
[26] P. Gupta, R. Padhee, P. K. Mahapatra, R. N. P. Choudhary, Structural, dielectric,
impedance and modulus spectroscopy of Bi2NdTiVO9 ferroelectric ceramics J Mater Sci:
Mater Electron 28, 17344 (2017)
[27] N. Shukla, V. Kumar, D. K. Dwivedi, Dependence of dielectric parameters and AC
conductivity on frequency and temperature in bulk Se90Cd8In2 Glassy Alloy, Journal of
Non-Oxide Glasses, 8, 47 (2016)
[28] N. Kumar, A. Ghosh, R. N. P. Choudhary, Electrical behavior of Pb(Zr0.52Ti0.48)0.5(Fe0.5
Nb0.5)0.5O3 ceramics, Materials Chemistry and Physics. 130, 381 (2011)
26

[29] O. Raymond, R. Font, N. Suárez-Almodovar, J. Portelles, J. M. Siqueiros, Frequency-
temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by
different precursors Part I. Structural and thermo-electrical characterization, J.Appl Phys. 97,
084107 (2005)
[30] D. K. Mahato, A. Dutta, T. P. Sinha Impedance spectroscopy analysis of double
perovskite Ho2NiTiO6, J Mater Sci 45, 6757 (2010)
[31] B. K. Das, T. Das, K. Parashar, S.K.S. Parashar, R. Kumar, H. K. Choudhary, V. B.
Khopkar, A.V. Anupama, B. Sahoo, Investigation of structural, morphological and NTCR
behaviour of Cu-doped ZnO nanoceramics synthesized by high energy ball milling, Materials
Chemistry and Physics 221,419 (2019)
[32] R. Das, R. N. P. Choudhary, Dielectric relaxation and magneto-electric characteristics of
lead-free double perovskite: Sm2NiMnO6, Journal of Advanced Ceramics 8, 174 (2019)
[33] R. Ranjan, R. Kumar, N. Kumar, B. Behera, R. N. P. Choudhary, Impedance and electric
modulus analysis of Sm-modified Pb(Zr0.55Ti0.45)1−x/4O3 ceramics, Journal of Alloys and
Compounds 509, 6388 (2011)
[34] S. Hajra, S. Sahoo, R. Das, R. N. P. Choudhary, Structural, Dielectric and Impedance
Characteristics of (Bi0.5Na0.5)TiO3-BaTiO3 Electronic System, Journal of Alloys and
Compounds.750, 507 (2018)
[35] S. Sahoo, P. K. Mahapatra, R. N. P. Choudhary, M. L. Nandagoswami, A. Kumar
Structural, electrical and magnetic characteristics of improper multiferroic: GdFeO3,
Mater.Res.Express.3,065017 (2016)
[36] T. Das, B. K. Das, K. Parashar, R. Kumar, H. K. Choudhary, A. V. Anupama, B. Sahoo,
P. K. Sahoo, S. K. S. Parashar, Effect of Sr-doping on sinterability, morphology, structure,
27

photocatalytic activity and AC conductivity of ZnO ceramics, J Mater Sci: Mater Electron,
DOI 10.1007/s10854-017-7198-6
[37] T. Rhimi, G. Leroy, B. Duponchel, K. Khirouni, S. Guermazi, M. Toumi, Electrical
conductivity
and
dielectric
analysis
of
NaH2PO4
compound,
Ionics
https://doi.org/10.1007/s11581-018-2494-6
[38] S. Kumar, J. Pal, S. Kaur, P. S. Malhi, M. Singh, P. D. Babu, A. Singh, The structural
and magnetic properties, non-Debye relaxation and hopping mechanism in
PbxNd1−xFeO3 (where x = 0.1, 0.2 and 0.3) solid solutions, Journal of Asian Ceramic
Societies 7,133 (2019)
[39] Y. B. Taher, A. Oueslati, N. K. Maalou, K. Khirouni, M. Gargouri, Conductivity
study and correlated barrier hopping (CBH) conduction mechanism in diphosphate
compound, Appl. Phys. A 120, 1537 (2015)
[40] R. Das, R. N. P. Choudhary, Structure, dielectric and electrical properties of relaxor
lead-free double perovskite: Nd2NiMnO6, Processing and Application of Ceramics 13,
1(2019)
[41] H. S. Mohanty, A. Kumar, B. Sahoo, P. K. Kurliya, D. K. Pradhan, Impedance
spectroscopic study on microwave sintered (1 − x) Na0.5Bi0.5TiO3–x BaTiO3 ceramics, J
Mater Sci: Mater Electron, doi.org/10.1007/s10854-018-8683-2
[42] V. Khopkar, B. Sahoo, Low temperature dielectric properties and NTCR behavior of
BaFe 0.5 Nb 0.5O3 double perovskite ceramic , Physical Chemistry Chemical Physics 22, 2986
(2020)
[43] R. Das, R. N. P. Choudhary, Structural, electrical, and leakage-current characteristics
of double perovskite: Sm2CoMnO6, Applied Physics A 125, 864(2019)
28