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Materials Science & Engineering B
journal homepage: www.elsevier.com/locate/mseb
Composite BNT-BT
0.08
/CoFe
2
O
4
with core-shell nanostructure for
piezoelectric and ferromagnetic applications
M. Cernea
a,
⁎
, B.S. Vasile
b
, I.V. Ciuchi
c,d
, V.A. Surdu
b
, C. Bartha
a
, A. Iuga
a
, P. Galizia
c
, C. Galassi
c
a
National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele 077125, Romania
b
University POLITEHNICA of Bucharest, 060042, Romania
c
National Research Council of Italy, Institute of Science and Technology for Ceramics (CNR–ISTEC), Via Granarolo 64, I-48018 Faenza, Italy
d
University “Al. I. Cuza”, Faculty of Physics, Bv. Carol I, Nr. 11, 700506 Iasi, Romania
ARTICLE INFO
Keywords:
Lead-free piezoelectric
((Bi
0.5
Na
0.5
)
0.92
Ba
0.08
TiO
3
)
Cobalt ferrite (CoFe
2
O
4
)
Sol-gel processes
Composite core-shell
ABSTRACT
In this work, we report on the synthesis and characterization of BNT-BT
0.08
/CoFe
2
O
4
biphasic composite with
core-shell structure. This artificial core (BNT-BT
0.08
)/shell (CoFe
2
O
4
) heterostructure was prepared by sol-gel
method and the resulting composite was characterized in term of microstructure, dielectric, piezoelectric and
magnetic properties. BNT-BT
0.08
/CoFe
2
O
4
sintered ceramic shows high permittivity (ε′ ≥ 30) and high dielectric
losses (tan δ ≥ 10) in the low frequency range (ν ≤ 10
4
Hz), remnant polarization (Pr) of ∼7.7 μC/cm
2
and,
remanent magnetization (Mr) of 24 emu/g at 5 K and of 14 emu/g, at room temperature. The present study
reveals that the ferroelectric, piezoelectric and magnetic properties of this new architectured composite depend
on the amount of each component and, can be tailored by adjusting their synthesis conditions. BNT-BT
0.08
/
CoFe
2
O
4
core-shell material investigated in this work provides a novel way to exploit new applications for the
multifunctional composite, such as piezoelectric sensor, magnetoelectronic sensors and data storage devices.
1. Introduction
In the last years, the core-shell nanomaterials have become a re-
search field of great interest due to their potential applications in var-
ious fields, like: catalysts, sensors, electronics, optoelectronics and
biomedical applications [1,2]. The composite materials consisting of
components with distinct properties have also attracted attention due of
their potential multifunctional applications [3–5]. New architectures as
core-shell composites are already used for some materials, as: bimetallic
core-shell nanomaterials [6,7], triple-layered core-shell structure (Au/
Co/Fe nanoparticles) [8], CoFe
2
O
4
/SiO
2
nanocomposite core-shell [9],
BNT-BTCe/SiO
2
core-shell heterostructure [10], etc. The design of the
new types of core-shell nanostructures is an important focus of research
and technological development. Here, we report on the core-shell na-
nostructure of lead-free piezoelectric BNT-BT
0.08
and ferromagnetic
CoFe
2
O
4
materials. BNT-BT
0.08
and CoFe
2
O
4
species can form compo-
sites which should combine their piezoelectric and magnetic properties.
These composites belong to the family of magnetoelectric multiferroic
materials that display both electric and magnetic order simultaneously
[11–15]. The resulting combination of magnetostrictive CoFe
2
O
4
with
piezoelectric BNT-BT
0.08
presents an artificial multiferroic composite
whose electric polarization can be tuned by a magnetic field and whose
magnetic properties can be altered by an electric field. An important
frontier in nanomaterials synthesis is the growth of crystalline stacked
layers on different nanostructures (as grains, layers, wires and tubes)
for acquiring controlled chemical and physical properties and new
functionalities [16].
In the present study, we describe the processes for the synthesis of
high-quality heterojunction BNT-BT
0.08
/CoFe
2
O
4
core-shell and we in-
vestigate its dielectric, piezoelectric and magnetic properties. This new
heterostructure was obtained using novel synthesis procedure based on
sol-gel chemistry. Different preparation protocols are used here, in
order to obtain nano-heterostructure containing BNT-BT
0.08
and
CoFe
2
O
4
and to improve its structural, ferroelectric and magnetic
properties. To the best of our knowledge, there are not reported studies
on the composite core-shell BNT-BT
0.08
/CoFe
2
O
4
. There are several
publications on each component (BNT-BT
0.08
and CoFe
2
O
4
), with na-
notube [17,18] and thin film [19,20] structure, part of core-shell
composites [19] and thin films heterostructures [21]. There are also,
few reports on hybrid piezoelectric/ferromagnetic structures, such as:
CoFe
2
O
4
/BaTiO
3
[22–26], Pb(Zr
0.52
Ti
0.48
)O
3
/NiFe
2
O
4
[27] and
NiFe
2
O
4
/BaTiO
3
[28] core-shell composites where, the authors studied
the influence of ferrite fraction variation on the magnetic properties of
the multiferroic core-shell –type nanostructures. Considering that the
https://doi.org/10.1016/j.mseb.2019.01.001
Received 28 September 2018; Received in revised form 15 November 2018; Accepted 4 January 2019
⁎
Corresponding author.
E-mail address: mcernea@infim.ro (M. Cernea).
Materials Science & Engineering B 240 (2019) 7–15
0921-5107/ © 2019 Elsevier B.V. All rights reserved.
T