Large electrostriction near the solubility limit in BaTi O3 -CaTi O3 ceramics

Article abstract of DOI:10.1063/1.1850598

This study prepared (1-x) BaTi O3 -xCaTi O3 (x=0.20-1.0) ceramics. Their structural and electric properties were analyzed. High electrostrictive strain of 0.22%, higher by 157% as compared to BaTi O3 ceramic, was obtained near the solubility limit in the side of composite (x=0.23), which is a diphasic ceramic composed of a ferroelectric tetragonal Ba0.8 Ca0.2 Ti O3 solid solution and a normal dielectric orthorhombic Ba0.07 Ca0.93 Ti O3 solid solution. This enhanced electrostriction resulted from the coupling of the large ionic polarization in Ba0.07 Ca0.93 Ti O3 with the non-180° domains in Ba0.8 Ca0. 2 Ti O3 during the external electric field exertion.

Full text of DOI:10.1063/1.1850598

Large electrostriction near the solubility limit in Ba Ti O 3 – Ca Ti O 3 ceramics
Xusheng Wang, Hiroshi Yamada, and Chao-Nan Xu
Citation: Applied Physics Letters 86, 022905 (2005); doi: 10.1063/1.1850598
View online: http://dx.doi.org/10.1063/1.1850598
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APPLIED PHYSICS LETTERS 86, 022905 (2005)
Large electrostriction near the solubility limit in BaTiO –CaTiO ceramics
3
3
a)
Xusheng Wang, Hiroshi Yamada, and Chao-Nan Xu
PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan
(
Received 19 July 2004; accepted 12 November 2004; published online 5 January 2005)
This study prepared ͑1−x͒BaTiO –xCaTiO ͑x=0.20–1.0͒ ceramics. Their structural and electric
3
3
properties were analyzed. High electrostrictive strain of 0.22%, higher by 157% as compared to
BaTiO ceramic, was obtained near the solubility limit in the side of composite ͑x=0.23͒, which is
3
a diphasic ceramic composed of a ferroelectric tetragonal Ba Ca TiO solid solution and a normal
0
.8
0.2
3
dielectric orthorhombic Ba0.07Ca0.93TiO solid solution. This enhanced electrostriction resulted from
3
the coupling of the large ionic polarization in Ba0.07Ca0.93TiO with the non-180° domains in
3
Ba Ca TiO during the external electric field exertion. © 2005 American Institute of Physics.
0
.8
0.2
3
[
DOI: 10.1063/1.1850598]
Piezoelectric/electrostrictive materials and actuators are
widely used in optics, astronomy, fluid control, and precision
machining due to their high generative force, accurate dis-
ramics. Large electrostrictive strain was obtained near the
solubility limit in the composite ceramics.
Our experiments prepared ͑1−x͒BaTiO –xCaTiO3 (x
3
1
placement, and rapid response. Practical materials with
=0.2, 0.23, 0.25, 0.30, 0.40, 0.5, 0.70, 0.90, 0.93, 0.95, and
1.0) ceramics using conventional solid-state reaction tech-
nique. Raw materials of BaCO (99.95%), CaCO (99.99%),
large piezoelectric/electrostrictive strain are mainly lead-
1
–3
based relaxor ferroelectric single crystals and ceramics.
3
3
With the recent growing demand of global environmental
protection, lead-free materials have attracted much attention.
and TiO (99.9%) (all supplied by Kojundo Chemical Lab.
2
Co.) were mixed with addition of alcohol, then dried and
heated at 900 °C for 4 h in air. Thereafter, they were re-
mixed and pressed into 10-mm-diam pellets and sintered at
1400 °C for 4 h in oxygen atmosphere. All samples had den-
sities that were greater than 95% of their theoretical values.
The sample crystallization behavior was examined using an
x-ray diffractometer (XRD, Rint2000; Rigaku Corp.) and a
scanning electron microscopy (SEM, S-4300; Hitachi Ltd.).
The sintered pellets were polished to 0.6 mm thickness. Sil-
ver electrodes were fired on both surfaces of the specimens
for electric measurement. Dielectric, ferroelectric, and elec-
trostrictive properties were characterized using an
impedance/gain-phase analyzer (HP4194A; Hewlett-Packard
Co.), an LCR tester (Hioki3522; Hioki E. E. Corp.), and a
ferroelectric analyzer (TF2000; aixACCT systems GmbH).
Using measured powder XRD patterns, the structures of
͑1−x͒BaTiO –xCaTiO ceramics were determined to be a
Barium titanate ͑BaTiO ͒ based materials showed promising
3
piezoelectric/electrostrictive properties. BaTiO single crys-
3
tals show large strain of around 1% despite their remarkable
4
–6
hysteresis;
and some doped BaTiO solid solutions also
3
7
–9
exhibit interesting piezoelectric/electrostrictive properties.
BaTiO was the first perovskite-type ferroelectric and
3
piezoelectric material developed and intensively studied ever
1
0
10–12
since its discovery 60 years ago. Early reports
revealed
that in the BaTiO –CaTiO system, Ca replaces Ba2+ in
2
+
3
3
BaTiO to form Ba Ca TiO solid solutions with x up to
3
1−x
x
3
0.21 and causes a negligible change of the Curie point (cubic
paraelectric–tetragonal ferroelectric transition temperature)
but strongly lowers the tetragonal–orthorhombic transition
temperature, which is of great value in improving the tem-
perature stability of piezoelectric/electrostrictive properties
for many practical applications. Above the solubility limit
3
3
͑
x=0.21͒, an insolubility region extends to 90 mol % of
pure tetragonal phase for x=0.20, tetragonal and orthorhom-
bic phase coexistence for x=0.23–0.90, and a pure ortho-
rhombic phase for x=0.93–1.0, respectively. Results of Ba-
rich extreme ͑x=0.20͒ and Ca-rich extreme ͑x=0.93–1.0͒
CaTiO , and further CaTiO added ͑Ͼ90 mol %͒, ortho-
3
3
rhombic CaTiO -based solid solutions were formed. No de-
3
tailed structural and electrical studies have been reported for
composite materials in the insolubility region ͑0.21Ͻx
Ͻ0.90͒. On the other hand, composite and diphasic materials
have been known to possess the potential for performance far
1
0–12
are similar to reported ones,
but a decrease is reported in
the solubility limit both for Ca addition in BaTiO and Ba
3
addition in CaTiO , which is possibly attributable to the high
3
1
3,1
beyond those of constituent materials.
based ultrahigh electrostriction
Pb͑Zn1/3Nb2/3͒TiO –PbTiO3
In fact, the lead-
purity of raw chemicals in our experiment. We have tried a
small amount (around 0.2%) of praseodymium substitution
in the ceramics and obtained an increase in solubility limit to
x=0.23 for tetragonal Ba1−xCaxTiO3 solid solution and to x
=0.90 for orthorhombic Ba1−xCaxTiO3 solid solution. Figure
1 shows refined XRD patterns for the tetragonal strongest
peak (110) [denoted as T(110)] and orthorhombic strongest
peak (121) [denoted as O(121)], and the related composition
dependence of interplanar distance as well. It shows that the
tetragonal (110) and orthorhombic (121) peaks for all
samples in the diphasic region ͑x=0.23–0.90͒ almost coin-
1
–3
materials
(PZN–PT)
like
and
3
Pb͑Mg1/3Nb2/3͒TiO –PbTiO (PMN–PT) are composition-
3
3
ally near the morphotropic phase boundary. Their high strain
is thought to result from the coupling between two equiva-
lent energy states, i.e., the tetragonal and rhombohedral
phases. This letter reports our results for dielectric, ferroelec-
tric, and electrostrictive properties in BaTiO –CaTiO ce-
3
3
a)
Also at: National Institute of Advanced Industrial Science and Technology,
07-1 Shuku, Tosu, Saga 841-0052, Japan; electronic mail: cn-
xu@aist.go.jp
cide, respectively, with those of tetragonal Ba Ca TiO
8
0.8
0.2
3
͑x=0.20͒ and orthorhombic Ba0.07Ca0.93TiO ͑x=0.93͒ solid
3
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003-6951/2005/86(2)/022905/3/$22.50 86, 022905-1 © 2005 American Institute of Physics
29.12.234.99 On: Mon, 15 Dec 2014 00:15:48
0
1

022905-2
Wang, Yamada, and Xu
Appl. Phys. Lett. 86, 022905 (2005)
FIG. 1. Refined XRD patterns of ͑1−x͒BaTiO –xCaTiO ceramics near the
3
3
tetragonal strongest peak (110) and orthorhombic strongest peak (121) (a),
and related interplanar distance d (b).
FIG. 2. Temperature and composition dependence of dielectric constant ␧
for the ͑1−x͒BaTiO –xCaTiO3 ceramics. (a) ␧ vs temperature for the x
3
=
0.23 sample at different frequency, (b) the peak value ␧max and width at
half-maximum (WHM) vs Ca fraction x, and (c) ␧ vs Ca fraction x at room
temperature.
solutions. From the above-mentioned result we can infer that
the ceramics, by present firing procedure and in composi-
tional range of 0.23ഛxϽ0.93, are in diphasic coexistence
and composed of tetragonal Ba Ca TiO solid solution
8
0
.8
0.2
3
50 kV/cm), again supporting the conjecture of interaction
and orthorhombic Ba0.07Ca0.93TiO solid solution. The back-
between the two phases in the composite ceramics. With in-
crease of added Ca, the remnant polarization and electrostric-
tive strain decreased and retained quite large values to x
=0.50, which are reasonable for the composite of ferroelec-
tric and normal dielectric materials but did not decrease
3
scattered scanning electron microscopy and energy-
dispersive x-ray spectrometry observations showed that
small (submicron) Ba0.07Ca0.93TiO grains dispersed among
3
the larger Ba Ca TiO grain matrix.
0
.8
0.2
3
1
4
Dielectric, ferroelectric, and electrostrictive properties
were measured with metal/ceramic/metal capacitors. Those
measurements are shown in Figs. 2–4. Figure 2 shows the
temperature and composition dependence of the dielectric
constant. Samples from x=0.20 to 0.50 have a similar tem-
perature dependence trend; for that reason, the dielectric con-
stant versus temperature plot is given only for sample x
greatly as did other similar composite materials. Figure 5
shows a comparison of the composition dependence of field-
induced strain ͑S͒, remnant polarization ͑P ͒, and piezoelec-
r
=
0.23 [Fig. 2(a)]. We found that Ca addition causes a negli-
gible change in the Curie point, lying around 120 °C, but a
decrease in peak height and an increase in width [Fig. 2(b)].
This fact implies that samples have relaxor features, which is
also implied by the peak shift with frequency in Fig. 2(a).
The dielectric constant in the composite phase ͑x
=
0.23–0.40͒ is higher than that in the pure ferroelectric
Ba Ca TiO ͑x=0.20͒ phase [Fig. 2(c)], unlike the simple
0
.8
0.2
3
mixture of two phases where the dielectric constant of the
1
3
composite lies between those of the individual phases. This
fact indicates that some interaction exists between the two
phases. Figures 3 and 4 show the polarization-electric field
hysteresis loops and electrostrictive displacement-electric
field butterfly curves for various compositional samples ͑x
=
0.20–0.50͒. The remnant polarization ͑P ͒ and electrostric-
r
tive strain (S: displacement divided by sample thickness)
show the largest values in the composite ceramic of x
=
0.23, in which the strain (0.22% at 50 kV/cm) is 157%
FIG. 3. Polarization vs electric field for various Ca fraction samples at room
temperature.
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higher than that in pure BaTiO3 ceramic (ϳ0.14% at
129.12.234.99 On: Mon, 15 Dec 2014 00:15:48

022905-3
Wang, Yamada, and Xu
Appl. Phys. Lett. 86, 022905 (2005)
are affected by surrounding domains, domain walls, and de-
fects, which are finally exhibited in the form of an internal
field. This local internal field overlaps on the external field
and improved or depressed the piezoelectric and electrostric-
tive properties depending on whether there is a plus or minus
interaction. In the present case, CaTiO is known as an in-
3
cipient ferroelectric and showed ferroelectric-like
1
5–17
features.
CaTiO and its solid solution Ba0.07Ca0.93TiO3
3
have large ionic polarization, thereby producing large dielec-
tric constants of about 160 and 200, respectively [Fig. 2(c)].
In the composite ceramics ͑x=0.23–0.50͒, Ba0.07Ca0.93TiO3
grains disperse among the ceramics; their ionic polarization
couples with the non-180° domains in surrounding ferroelec-
tric Ba Ca TiO grains. The polarization enhances the po-
0
.8
0.2
3
larizability and domain rotation ability of the ceramics dur-
ing the external electric field exertion. Therefore, the related
parameters like dielectric constant, remnant polarization,
electrostrictive strain, and piezoelectric coefficient of the ce-
ramics increase. On the other hand, the ferroelectric proper-
ties of the composite are degraded by non-ferroelectric addi-
tion. Behaviors of the physical parameters in Fig. 2(c) and
Fig. 5 are a result of a compromise between these two ef-
fects.
FIG. 4. Field-induced displacement for various Ca fraction samples with
50 kV/cm, 1 Hz driving field at room temperature (sample thickness is
.6 mm).
±
0
In summary, high dielectric, ferroelectric, piezoelectric/
electrostrictive properties were obtained in the composite of
͑1−x͒BaTiO –xCaTiO ceramics near the solubility limit. In
tric coefficient ͑d ͒, where the latter parameter is an intrinsic
3
3
physical parameter of the material and calculated by d33
3
3
2
=
2Q␧␧ P . Here Q=S/P is the electrostrictive coefficient; ␧
the diphasic region ͑xജ0.23͒, the coupling of the large ionic
0
s
and ␧ are the relative and vacuum dielectric constants; P
polarization in Ba0.07Ca0.93TiO with the non-180° domains
0
3
and P are the polarization and spontaneous polarization.
s
in Ba Ca TiO seems to act as an important factor in im-
0
.8
0.2
3
The above-mentioned result can be explained as follows.
proving ceramic properties. Our material is similar to the
high-strain MBP material to some extent, but ours is a com-
posite of ferroelectric and nonferroelectric materials, imply-
ing a route to develop new high-strain materials in a wide
range of different material families.
In the ͑1−x͒BaTiO –xCaTiO ͑x=0.20–0.90͒ ceramics, the
3
3
structure is a diphasic composite of the tetragonal
Ba Ca TiO solid solution and orthorhombic
0
.8
0.2
3
Ba0.07Ca0.93TiO solid solution for xജ0.23, the former is a
3
ferroelectric, while the latter is a normal dielectric in a large
range of temperatures, including our investigated tempera-
ture range ͑−180–120 °C͒. Large electrostrictive strain is
believed to originate from the non-180° domain rotation
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FIG. 5. Composition dependence of strain and piezoelectric coefficient in a
±
50 kV/cm driving field.
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1