Available online at www.sciencedirect.com
CERAMICS
INTERNATIONAL
Ceramics International 41 (2015) 4789–4797
www.elsevier.com/locate/ceramint
Electric field induced polarization and strain
of (Bi1/2Na1/2)TiO3–BaTiO3 ceramics
Jeong-Ho Chon, Chang-Jun Jeon, Ku-Tak Lee, Jung-Soo Park, Young-Hun Jeong, Ji-Sun Yun
Intelligent Electronic Component Team, Korea Institute of Ceramic Engineering and Technology, Seoul 153-023, Republic of Korea
Received 12 September 2014; received in revised form 3 December 2014; accepted 7 December 2014
Available online 12 December 2014
Abstract
This study investigated the whole composition range of the electric field induced polarization and strain of (1x)(Bi0.5Na0.5)TiO3–xBaTiO3
ceramics fabricated by a conventional solid-state reaction. In most of the composition regions (xo0.7) except for the MPB region (0.06rxo0.08),
saturated square-shape P–E loops and large negative strains in the S–E curves, along with a high coercive field and a large remnant polarization,
were obtained. In these composition ranges, the remnant polarization and maximum positive strain decreased gradually with an increasing BaTiO3
content and the coercive field reached the maximum at x¼ 0.4. The high coercive field was intrinsically affected by (Bi0.5Na0.5)TiO3, possessing a
doubling of the unit cell owing to octahedron tilting and compositional ordering. At 0.7rx, the crystal structure became a simple tetragonal
structure, and the remnant polarization and the coercive field significantly decreased with an increasing BaTiO3 content.
& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: A. Sintering; C. Ferroelectric properties; D. Perovskites; E. Actuator
1. Introduction
Piezoelectric ceramics have dominated the commercial market for electromechanical devices, such as sensors and actuators.
The most prominent and widely used piezoceramics are lead–
zirconate–titanate (PZT)-based perovskite oxides. With public
opinion driving a worldwide trend toward greater environmental
responsibility, however, the need for lead-free devices in electronic components and systems continues to receive significant
attention within the electronics industries. Bolstered by regulatory and competitive pressures, customers are demanding leadfree RoHS compatible parts, and industries are adopting predominantly lead-free RoHS compatible solutions.
(Bi0.5Na0.5)TiO3 (BNT) is an A-site substituted distorted perovskite compound, with a rhombohedral (R3c) phase with a pseudocubic perovskite cell at room temperature. BNT is widely known as
a representative of lead free materials that possesses strong ferroelectric properties and high mechanical strength at room temperature:
a large remnant polarization, Pr ¼ 38 μC/cm2; a coercive field of
n
Corresponding author. Tel.: þ82 2 3282 2424; fax: þ 82 2 3282 7816.
E-mail address: goedc@kicet.re.kr (J.-H. Cho).
http://dx.doi.org/10.1016/j.ceramint.2014.12.032
0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Ec ¼ 73 kV/cm; a piezoelectric constant, d33 ¼ 72.9 pC/N; and high
Curie temperature (320 1C) [1–7].
BaTiO3 (BT) is one of the most extensively studied ferroelectric
materials with a perovskite structure. Superior ferroelectric properties and a high dielectric constant make BaTiO3 useful in an array
of applications, such as multilayer ceramic capacitors (MLCs),
ferroelectric memory devices, and piezoelectric transducers [11].
The ferroelectric phase at room temperature is tetragonal (P4mm)
with oxygen and titanium ions shifting to produce a spontaneous
polarization, exhibiting both displacive soft-mode phonons and
order–disorder behavior in the phase transition.
Recently, (Bi0.5Na0.5)TiO3–BaTiO3 (BNT–BT) solid solutions
are expected to be a promising alternative for lead-free piezoelectric ceramics as well as lead-free positive temperature coefficient (PTC) ceramics [9–17]. A semiconducting BNT–BT system
has been proposed as a new lead-free PTC thermistor material
[18–20]. These studies indicated that incorporation of the BNT
phase into BT ceramics is an effective way to enhance the PTC
properties. In particular, a resistivity anomaly of BT ceramics with
20 mol% BNT starts at around 210 1C [18]. Furthermore, the
(1 x)BNT–xBT solid solution has attracted considerable attention
on account of the existence of a morphotropic phase boundary
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J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
(MPB) at 0.06rxr0.08, which offers quite a large electric fieldinduced strain [9,21] and causes significant enhancements in the
ferroelectric and piezoelectric properties [22,23]. It has been
considered to be a superior lead-free candidate to replace lead-contained materials to increase the Curie temperature of BaTiO3-based
ceramics [8].
The performance of electromechanical devices is definitely
governed by the electric field induced strain of the materials.
BNT–BT ceramics with MPB composition exhibit highly
effective d33, Smax/Emax ¼ 700 pm/V, at 6 kV/mm [24] and a
large-strain behavior, particularly in the vicinity of the
depolarization temperature [25,26]. In the recent years, many
groups have demonstrated the physical mechanism of an
electric-field-induced large strain. Zhang et al. [27,28] suggested that giant strains in the Bi0.5Na0.5TiO3–BaTiO3–
K0.5Na0.5NbO3 system are due to the structural phase transition
between antiferroelectric and ferroelectric. In Pb(Zr,Sn,Ti)O3based antiferroelectric ceramics, large electric field-induced
strains were also described as transforming the antiferroelectric
phase near the AFE and FE phase boundary to the ferroelectric
phase by an externally applied field [29]. Hiruma et al. [30]
and Teranishi et al. [31] reported that non-1801 domain
switching of a field-induced phase gives rise to large strains
detected by the X-ray diffraction pattern under a high electric
field. Dittmer et al. [15] suggested that the large strain in
(Bi0.5Na0.5)TiO3–0.06BaTiO3 was the field induced transition
from an ergodic relaxor state to a ferroelectric phase, in which
the electric field thereby developed macrodomains from polar
nano regions. This transition to a long range order was accompanied by a large increase in strain. With the decrease of the
electric field the ferroelectric order collapses, resulting in
virtually zero remanent polarization and strain. This lack of
remanence gave rise to large unipolar strains that could be harvested during each cycle. Despite many studies, however, there
still remains controversy concerning the origin of giant strains.
The ferroelectric properties and crystal structures of (1 x)
BNT–xBT solid solutions have been extensively reported
[22,32–35]. The majority of the studies have focused on the
BNT-rich (0.06 r xr 0.08) region for piezoelectric applications and the BT-rich region (x Z 0.9) for PTC applications.
Furthermore, there is no information about the strain and polarization behaviors over the whole composition range of BNT–
BT, although a few groups reported their crystal structures and
properties over fairly wide ranges [36–39]. In this study, we
report the electric field induced strains and hysteresis loops of
polarization in a series of (1 x)(Bi0.5Na0.5)TiO3–xBaTiO3
(x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60,
0.70, 0.80, and 0.90), which is expected to be of practical
importance as a lead-free material for extensive applications.
2. Experimental
(1 x)(Bi0.5Na0.5)TiO3–xBaTiO3 powders were synthesized
using the solid state reaction method in an air atmosphere. The
compositions of these solid solutions were prepared with
x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60,
0.70, 0.80, and 0.90. Reagent grade (4 99.0% purity) Bi2O3,
Na2CO3, BaCO3 and TiO2 supplied by Sigma-Aldrich, USA
were used as starting materials. The starting materials were
prepared after removing absorbed water completely at 200 1C
for one hour; special care was taken so that the raw materials
did not absorb water during the manufacturing process. The
powders were weighed according to the chemical formula,
ball-milled for 24 h in anhydrous ethanol, and calcined at
850–1050 1C for 2 h. Polyvinyl alcohol was added as a binder
to the calcined powder, which was then pressed into circular
disks with a diameter of 10 mm at 100 MPa. The green compacts were sintered in covered alumina crucibles at 1150–
1300 1C for 2 h in air. The calcination temperature and sintering temperature were increased with an increasing BaTiO3
content. The samples were then lapped to 1.0 mm thickness
and electroded by applying a silver paste onto both surfaces.
The strain–electric field (S–E) curves and polarization–
electric field (P–E) hysteresis loops were measured using a
ferroelectric test system (Radiant P-LC-K, USA) at room
temperature at a frequency of 1 Hz. Temperature dependence
of the dielectric constant was performed in a temperature range
between room temperature and 300 1C using a precision LCR
meter (Model 4284A, Agilent, USA). The remnant polarization and the coercive field were evaluated at zero field and at
zero polarization in the P–E hysteresis loop, respectively.
3. Results and discussion
According to our recent work with (1 x)BNT–xBT ceramics, the ferroelectric behaviors of polarization and strain may
be divided into five regions based on the temperature dependence of the relative dielectric permittivity (εr) and a crystal
structure: (a) very low BT content (x o 0.06), (b) MPB region
(0.06 r x o 0.15), (c) 0.15r x o 0.4, (d) 0.40 r xo 0.7, and
(e) high BT content (0.7 r x ) [40].
Fig. 1 shows the polarization versus electric field (P–E)
hysteresis loops and the strain versus electric field (S–E) curves
at x ¼ 0.03, along with coercive fields and remnant polarizations evaluated from P–E loops. The saturated square-shape
P–E loops and the large negative strains in S–E curves are
considered as a typical normal ferroelectric behavior. In addition, a high coercive field (Ec, 4.98 kV/cm) and a large remnant polarization (Pr, 31.6 μC/cm2) were measured at the applied electric field of 8 kV/cm, which agrees well with the
existing experimental results [41].
P–E hysteresis loops and S–E curves in MPB region
(0.06 r x r 0.08) are shown in Fig. 2. In a similar maximum
polarization (31.3 μC/cm2 at 6 kV/mm) to Fig. 1, the coercive
field, the remnant polarization, and the negative strain were
significantly reduced to 1.4 kV/mm, 13 μC/cm2, and below
0.01% at x ¼ 0.08, respectively. The strain behavior in MPB
region has been described by the field induced transition from
an ergodic relaxor state [42,43] to a ferroelectric state, developing macrodomains from polar nano regions [44]. This transition leads to a large positive strain, along with a small remnant polarization and negative strain due to the ferroelectric
order collapses at a zero electric field [15]. According to Jo
et al. [45] and Ullah et al. [46], these results may suggest that
40
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-5
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20
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Electric field(V/mm)
Electric field (V/mm)
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4kV/mm
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7kV/mm
8kV/mm
0.08
0.06
4kV/mm
5kV/mm
6kV/mm
0.10
0.08
0.04
Strain(%)
Strain (%)
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5kV/mm
6kV/mm
30
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Polarization(μC/cm )
2
Polarization (μC/cm )
J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
0.02
0.00
-0.02
0.06
0.04
0.02
-0.04
0.00
-0.06
0
-0.02
2000 4000 6000 8000 10000
-6000
-4000
Electric field (V/mm)
-2000
0
2000
Electric field(V/mm)
6
40
2.5
14
30
25
Ec
4
20
Pr
15
3
10
5
2
2.0
Coercive Field (kV)
Coercive Field (kV)
5
2
2
Remnant Polarization ( μC/cm )
35
12
Pr
10
1.5
8
Ec
1.0
6
4
0.5
0
1
4
5
6
7
8
-5
Electric Field (kV/mm)
Remnant Polarization ( μC/cm )
-10000 -8000 -6000 -4000 -2000
2
0.0
3.5
4.0
4.5
5.0
5.5
6.0
0
6.5
Electric Field (kV/mm)
Fig. 1. (a) P–E hysteresis loops, (b) S–E curves, and (c) coercive fields and
remnant polarizations of (1 x)BNT–xBT ceramics at x ¼0.03.
Fig. 2. (a) P–E hysteresis loops, (b) S–E curves, and (c) coercive fields and
remnant polarizations of (1 x)BNT–xBT ceramics at x¼ 0.08.
two polarization states, a ferroelectric and a non-polar state,
coexist in this composition range and their free energies are
comparable at a zero electric field. In addition, they reported
that the slightly pinched P–E hysteresis loops in the MPB
composition may be attributed to the possible existence of nonpolar regions. However, a pinched P–E hysteresis loop can
also be induced by the combination of the switching of the
dipoles resulting from oxygen vacancies and a ferroelectric
domain switching [47,48]. There still remains controversy concerning the cause of pinched P–E hysteresis loops.
Fig. 3 shows P–E hysteresis loops and S–E curves at x¼ 0.12,
presenting well-saturated P–E loops and butterfly-shaped loops
with large negative strains. These behaviors may appear to be a
typical normal ferroelectrics with a first order transition behavior.
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J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
ceramics have been categorized as relaxor ferroelectrics. Relaxors
are a class of disordered cystals that possess peculiar structure and
properties. At sufficiently low temperature (Tf, which is typically
0.12
40
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30
25
20
15
10
5
0
-5
-10
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4kV/mm
5kV/mm
6kV/mm
7kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
0.10
0.08
0.06
Strain(%)
2
Polarization(μC/cm )
In Fig. 4, however, (1 x)BNT–xBT ceramics with x¼ 0.12
exhibited a strong frequency dispersion of the dielectric constant
(εr), which implies that they are relaxors. Thus, BNT–BT
0.04
0.02
0.00
-0.02
-0.04
-0.06
-10000 -8000 -6000 -4000 -2000
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8000 10000
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Electric field(V/mm)
-2000
0
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Electric field(V/mm)
Fig. 3. (a) P–E hysteresis loops and (b) S–E curves of (1 x)BNT–xBT ceramics at x¼ 0.12.
8000
Relative Dielectric Constant (εr)
Relative Dielectric Constant (εr)
7000
6000
100 kHz
5000
10 kHz
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1 kHz
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1 MHz
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6000
100 kHz
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10 kHz
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1 kHz
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1 MHz
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o
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o
Temperature ( C)
Temperature ( C)
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12000
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100 kHz
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Relative Dielectric Constant (εr)
Relative Dielectric Constant (εr )
14000
6000
5000
1 kHz 10 kHz
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100 kHz
0
50
100
150
200
o
Temperature ( C)
250
300
0
50
100
150
200
250
o
Temperature ( C)
Fig. 4. The frequency dispersion of dielectric constant (εr) of (1 x)BNT–xBT ceramics with (a) x ¼0.08, (b) x ¼0.12, and (c) x¼ 0.15.
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J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
40
20
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
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0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
-0.06
BNT-0.20BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
-0.08
-10000 -8000 -6000 -4000 -2000
8000 10000
Electric field(V/mm)
40
20
0
2000
4000
6000
8000 10000
Electric field(V/mm)
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
BNT-0.20BT
0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
-0.06
BNT-0.40BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
8000
10000
Electric field(V/mm)
40
20
0
2000
4000
6000
8000 10000
Electric field(V/mm)
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
BNT-0.40BT
-0.08
-10000 -8000 -6000 -4000 -2000
0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
BNT-0.60BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
8000 10000
Electric field(V/mm)
-0.06
BNT-0.60BT
-0.08
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
8000 10000
Electric field(V/mm)
Fig. 5. P–E hysteresis loops and S–E curves at (a) x¼ 0.20, (b) x¼ 0.40, and (c) x ¼0.60.
hundreds degrees below the so-called Burns temperature (TB)),
the polar nanoregions (PNRs) in the canonical relaxors become
frozen into a nonergodic state and are being irreversibly
transformed into a ferroelectric state through a sufficient strong
external electric field. The PNRs could be considered to be a
result of local phase transitions or phase fluctuations; thus, the
crystal consists of nanosized polar islands that are embedded
into a cubic matrix in which the symmetry remains unchanged
[42]. Although the absence of Td (depolarization temperature) in
Fig. 4(a) and (b) could characterize them as ergodic relaxors, in
which the field-induced strains are recovered to their initial state
with the removal of electric field, it might be considered that the
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J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
Table 1
The remnant polarization, the maximum positive strain, and the coercive field of BNT–xBT ceramics measured at 8 kV/mm.
BT content (x)
Remnant polarization (Pr) (μC/cm2)
Maximum positive strain (%)
Coercive field (Ec) (kV/mm)
40
20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
24.34
0.099
4.28
23.19
0.083
4.699
20.56
0.081
4.88
20.54
0.079
4.70
19.58
0.074
4.60
17.36
0.065
4.07
17.01
0.081
3.05
13.35
0.064
1.85
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
0.20
0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
-0.06
BNT-0.70BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
8000
Electric field(V/mm)
40
20
0
2000
4000
6000
8000
10000
Electric field(V/mm)
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
BNT-0.70BT
-0.08
-10000 -8000 -6000 -4000 -2000
10000
0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
-0.06
BNT-0.80BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
4000
6000
8000
10000
Electric field(V/mm)
40
20
0
2000
4000
6000
8000
10000
Electric field(V/mm)
0.12
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
4kV/mm
5kV/mm
6kV/mm
7kV/mm
8kV/mm
0.10
0.08
0.06
10
Strain(%)
2
Polarization(μC/cm )
30
BNT-0.80BT
-0.08
-10000 -8000 -6000 -4000 -2000
0
-10
0.04
0.02
0.00
-0.02
-20
-0.04
-30
BNT-0.90BT
-40
-10000 -8000 -6000 -4000 -2000
0
2000
Electric field(V/mm)
4000
6000
8000 10000
-0.06
BNT-0.90BT
-0.08
-10000 -8000 -6000 -4000 -2000
0
2000
Electric field(V/mm)
Fig. 6. P–E hysteresis loops and S–E curves at (a) x¼ 0.70, (b) x¼ 0.80, and (c) x ¼0.90.
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J.-H. Cho et al. / Ceramics International 41 (2015) 4789–4797
0.88BNT–0.12BT ceramics possess a sufficiently large amount
of PNRs to irreversibly transform to the phase with the ferroelectric order through an electric field.
With a further increasing BT content over 0.15%, a phase
transition between unknown tetragonal structures was observed
at around x¼ 0.4, and this phase subsequently transformed to
tetragonal with the space group P4mm at around x¼ 0.7 [40].
The temperature dependence of phase transitions in the composition range from x¼ 0.4 to 0.7 exhibited normal displacive
transition behaviors. In contrast, the canonical relaxor phase
transition with a diffuse phase transition (DPT) that results from
a compositional disorder appeared clearly at x40.7, in particular at x¼ 0.9, as depicted in Fig. 4(d).
Fig. 5 shows P–E hysteresis loops and S–E curves at
x ¼ 0.20, 0.40, and 0.60 and Table 1 summarizes the remnant
polarizations, the maximum positive strains, and the coercive
fields at 0.20 r xr 0.90 when an electric field of 8 kV/mm is
applied. The remnant polarization and the maximum positive
strain decreased gradually with an increasing BT content in
this composition range, and the coercive field reached the maximum value at x¼ 0.40, at which the phase transition between
tetragonal phases occurred.
Fig. 6 shows P–E hysteresis loops and S–E curves at
x ¼ 0.70, 0.80, and 0.90. With an increasing BT content, the
remnant polarization and the coercive field significantly decreased. In many previous reports, BNT–BT ceramics typically
exhibited a large strain, a fat hysteresis and, in particular, a
large coercive field.
The important features in ferroelectric ceramics are the field
induced polarization and strain. From a practical point of view,
the coercive field should be the center of attention because it is
directly related to the operating voltage of the device. These
extrinsic contributions are described by domain processes and
reorientations. Likewise, a coercive field is definitely associated with domain motion. Kim et al. [49] simplified the coercive field for domain motion at the domain wall center based
on the Ginzburg–Landau–Devonshire theory. Even though
they assumed a ferroelectrics with a second order phase transition and the presence of preexisting 1801 domain walls with
finite wall widths, their theoretical estimation is fairly acceptable to explain the relationship between a coercive field and a
lattice parameter. According to their calculation, the coercive
field for domain motion is proportional to a lattice parameter
and a spontaneous polarization and inversely proportional to
domain width. BNT–BT ceramics experience a rhombohedral–
tetragonal phase transition at 0.06 r xr 0.08 and another
phase transition between unknown tetragonal structures at
around x ¼ 0.4 [40]. In BNT at room temperature, the Na/Bi
and Ti atoms are displaced parallel to each other along the
[111] direction to give a polar ferroelectric phase. At the same
time, the oxygen octahedra are tilted about [111] with antiphase tilts, giving rise to doubling of the unit-cell axes. At
320 1C, there is the tetragonal phase (P4bm), in which Na/Bi
and Ti atoms are displaced in opposite directions along the
polar [001] axes, combined with in-phase tilts of oxygen
octahedra, which result in cell doubling in the [100] and [010]
directions [7]. The doubling of the unit-cell agrees well with an
4795
ion-ordering point of view, from which the first order transition
behaviors of the BNT–BT system at 0.15 rx r 0.7 are the
evidence of the cation or vacancy ordering in the A-site of the
perovskite structure. The degree of ordering decreases with an
increasing Ba content, and a second order transition behavior
appear at x4 0.7. Therefore, we assume that the large coercive
field of the BNT–BT system is an intrinsic property owing to
the doubling of the unit-cell, and the phase transition to a
simple tetragonal structure at x 4 0.7 leads to the decrease of
the coercive field.
4. Conclusions
We fabricated (1 x)(Bi0.5Na0.5)TiO3–xBaTiO3 ceramics over
the whole composition range by a conventional solid-state reaction
and investigated the electric field induced polarization and strain.
The ferroelectric behaviors based on their composition were
divided into five regions: (a) very low BT content (xo0.06), (b)
MPB region (0.06rxo0.15), (c) 0.15rxo0.4, (d) 0.40r
xo0.7, and (e) high BT content (0.7rx). In the very low BT
content region (xo0.06), we obtained saturated square-shape P–E
loops and the large negative strains in the S–E curves, along with a
high coercive field and a large remnant polarization. In MPB
region, there was a nearly zero negative strain (a large positive
strain) and a small remnant polarization, demonstrating the field
induced transition from a relaxor state to a ferroelectric state. At
x¼ 0.12, even though there were well-saturated P–E loops and
butterfly-shaped loops with large negative strains, frequency
dispersion of the dielectric constant was also observed, which
implies that it is a relaxor possesses a sufficiently large amount of
PNRs to irreversibly transform to the phase with the ferroelectric
order through an electric field. In the composition range of
0.15rxo0.7, the remnant polarization and the maximum positive strain decreased gradually with an increasing BT content, and
the coercive field reached maximum at x¼ 0.4. We assumed that
the ferroelectric properties of (1 x)BNT–xBT ceramics at xo0.7,
in particular a high coercive field, were intrinsically affected by
BNT, which possessed the doubling of a unit cell owing to
octahedron tilting and cation (or vacancy) ordering. With a high
BT content (0.7rx), the crystal structure transformed to a simple
tetragonal structure so that the remnant polarization and the
coercive field significantly decreased with an increasing BT
content.
Acknowledgments
This work was financially supported by a grant from the R&D
program for the strategic core materials funded by the Ministry of
Trade, Industry and Energy, Republic of Korea.
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ID
1460360
Title
Electricfieldinducedpolarizationandstrainof(Bi1/2Na1/2)TiO3–BaTiO3ceramics
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