Improved Multiferroic Properties in x(BiFeO3)-(1x)(Bi0.5Na0.5TiO3) (x = 0, 0.05, 0.10, 0.15 and 0.20)
Ceramics
T. Durga Rao, T. Karthik, M. Ramalingeswara Rao, Saket Asthana*
Advanced Functional Materials Laboratory, Department of Physics,
Indian Institute of Technology Hyderabad, Andhra Pradesh – 502205, India
Corresponding author’s e-mail: asthanas@iith.ac.in, Tel.: 040-23016067; Fax: +91 40 2301 6032.
*
Abstract
Tuning the multiferroic properties of BiFeO3was carried out
by forming solid solution x(BiFeO3)-(1-x)(Bi0.5Na0.5TiO3) x =
0, 0.05, 0.10, 0.15 and 0.20 using solid state route. XRD
pattern of all compounds shows rhombohedral crystal
structure with R3c space group. Magnetic measurements
reveal that weak ferromagnetism is induced in the compounds
with x = 0.05, 0.10 and 0.15 due to the structural distortions.
Grain and grain boundary contributions were estimated from
the Nyquist’s plots. Activation energies measured from
temperature dependant ac conductivity measurements revealed
that electronic conduction and oxygen vacancy movements are
the prime contributors to the conductivity.
.
Keywords: Multiferroics, weak ferromagnetism, ac
conductivity, activation energy.
Introduction
Multiferroic materials have become promising for
technological applications due to simultaneous
existence of ferroic orders such as ferroelectric,
(anti)ferromagnetic and/or ferroelastic orders [1].
BiFeO3 is a fascinating multiferroic among all the
materials due to its high Curie temperature (TC =
1103K) and high Neel temperature (TN = 643K).
However, the presence of leakage current and
antiferromagnetic nature limits its potential as a material
of choice for device applications. Thus the reduction of
leakage current and inducement of ferromagnetism in
BiFeO3 is highly desirable. Making solid solution with
ferroelectric materials like BaTiO3, Bi0.5Na0.5TiO3
improves both ferroelectric and magnetic properties of
BiFeO3.
Experimental details
Conventional solid state route was used to synthesize
x(BiFeO3)-(1-x)(Bi0.5Na0.5TiO3), x = 0 [BFO], 0.05
[BNFTO5], 0.10 [BNFTO10], 0.15 [BNFTO15] and
0.20 [BNFTO20] ceramics. The Phase analysis of the
compounds were examined by an X-ray diffractometer
(Panalytical X’pert Pro) with Cu Kα radiation (λ=1.5406
Å). Magnetic properties were measured using PPMS
with VSM assembly (Quantum Design, USA).
Electrical properties were measured using Wayne Kerr
6500B impedance analyzer.
Results and discussion
All the X-ray diffraction patterns were refined using
Fullprof software by considering R3c space group as a
model. In BFO, G-type antiferromagnetic ordering
superimposed with spiral modulated spin structure
(SMSS). The SMSS is suppressed by crystal distortion
as is evident from the appearance of weak
ferromagnetism in the magnetization curves in the
BNFTO compounds. Magnetic anomaly has been
observed from the ZFC and FC curves (measured at
1000 Oe) in all the compounds near 280K. The sharp
increase in magnetization below 35K reveals that the
development of incommensurate magnetic structure
(SMSS) in all the compounds.
Frequency variation of real part of impedance (Z′)
for BFO and BNFTO indicates that the compounds
exhibit Negative temperature coefficient of resistance
(NTCR) character. Increase in Z′ value in BNFTO
compound suggests that an enhancement of the bulk
resistance of the compounds [3].
The frequency dependence of ac conductivity obeys
Joncher’s power law [2]:
(1)
 a.c   (0)  A s
where σ(0) is the dc conductivity and s is a power law
exponent.
Activation energies are calculated at different
frequencies in the measured temperature range (30 oC –
400 oC). Activation energies decrease with the increase
of frequency. Electronic hopping, oxygen vacancies
movement and/or creation of defects contribute to
conduction in all the compounds.
Acknowledgement
Authors are grateful to the Department of Science and
Technology (DST), India for their financial support
under Fast Track scheme (SR/FTP/PS–065/2011) to
carry out this work.
References
[1] W. Eerenstein, N.D. Mathur , J.F.Scott,
‟Multiferroic and magnetoelectric materials”, Nature,
442, 759 (2006).
[2] A. K. Jonscher, ‟The ‘universal’ dielectric
response”, Nature. 267 (1977) 673.
[3] T.D. Rao, T. Karthik, A. Srinivas, S. Asthana,
‟Study of structural, magnetic and electrical properties
on Ho-substituted BiFeO3”, Solid State Commun., 152,
2071 (2012).