Effect of Nano-Sized Y2O3 Doping on the Electrical Properties of (Ba0.90Ca0.10)(Ti0.9Sn0.1)O3 Ceramics

Article abstract of DOI:10.1002/pssa.201700417

Well dispersed Y₂O₃ nanoparticles are prepared by azeotropic co-precipitation method. (Ba_0.90Ca_0.10)(Ti_0.9Sn_0.1)O₃ lead-free piezoelectric ceramics doped with the nano-sized Y

Full text of DOI:10.1002/pssa.201700417

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ORIGINAL PAPER
Piezoelectric Properties
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Effect of Nano-Sized Y2O3 Doping on the Electrical
Properties of (Ba0.90Ca0.10)(Ti0.9Sn0.1)O3 Ceramics
Zhi-hui Chen,* Zhi-wei Li, Jian-hua Qiu, Tian-xiang Zhao, Ke-qin Zhu,
Jian-ning Ding, Wei-qin Zhu, and Jiu-jun Xu*
(Ti0.90Sn0.10)O3 (BCTS) ceramics, and
found that the A-site substitution restrains
abnormal grain growth and leads to the
formation of homogeneous microstruc-
tures during sintering.[15–17] Besides piezo-
electric constant, more properties should
be considered for real application such as
dielectric properties and thermal stability.
The effects of nano-sized particles on
dielectric properties are interesting due
to the confinement of charge carriers in
such particles are expected to produce.[18]
The addition of nano-sized oxides
in zirconium matrix has been reported
Well dispersed Y2O3 nanoparticles are prepared by azeotropic co-precipita-
tion method. (Ba0.90Ca0.10)(Ti0.9Sn0.1)O3 lead-free piezoelectric ceramics
doped with the nano-sized Y2O3 (BCTZY, x ¼ 0.01–0.09%) are synthesized at
1460 ꢀC for 2 h via solid-state sintering method. X-ray diffraction suggests
typical perovskite structure of all the compositions. The addition of the
nano-Y2O3 results in the improvement in dielectric and piezoelectric
properties. The optimized piezoelectric properties is obtained at x ¼ 0.01
with d33 of 596 pC/N and Kp of 57.1%, respectively.
to
lead
better
high
tempera
1. Introduction
ture stability due to the grain boundary
pinning.[19] However, few studies were made to ascertain the
influence of nano-sized Y2O3 on the dielectric and piezoelectric
properties of the BT based ceramics. In our previous work, a
modified co-precipitation method was developed, in which an
azeotropic distilling process was introduced to replace the
traditional ethanol washing process. Agglomerate-free nano-
powders such as Y3Al5O12 and Bi4Ti3O12 were prepared.[20–22]
In this work, well dispersed Y2O3 nanoparticles were
prepared by the azeotropic co-precipitation method. Then the
nano-sized Y2O3 was doped into the BCTS ceramics via solid-
state sintering method. The phase structure, microstructures,
dielectric properties and piezoelectric properties of the
(Ba0.90Ca0.10)(Ti0.9Sn0.1)O3ꢁxY2O3 (BCTSY) ceramics were
studied.
In recent years, BaTiO3 have attracted much attention as one of
the good candidates to substitute for the lead based piezo-
electrics.[1–3] However the maximum piezoelectric constant d33
reported for BaTiO3 ceramics by conventional sintering is
190 pC/N.[4] Xue et al. discovered Ca2þ and Sn4þ ions co-doped
BaTiO3 based system and d33 reached to 530 pC/N.[5] Hereafter,
(Ba, Ca) (Ti, Sn) O3 (BCST) ceramics with high d33 of 578 pC/N
was developed.[6] The addition of rare earth oxides (Re2O3) such
as La2O3, CeO2, Dy2O3, and Y2O3 is effective on the improvement
of piezoelectric properties.[7–11]. Y2O3 is widely used as a
sintering aid, which significantly facilitates the densification
process by enhancing the diffusivity of atoms and lowering the
sintering temperature.[12–14] In our previous work, we made an
systematically study on Re2O3 doping in the (Ba0.90Ca0.10
)
Prof. Z.-H. Chen, Dr. Z.-W. Li, Prof. J.-H. Qiu, Dr. T.-X. Zhao,
Dr. K.-Q. Zhu, Prof. J.-N. Ding
School of Materials Science and Engineering
Jiangsu Collaborative Innovation Center of Photovolatic Science and
Engineering
2. Experimental Section
Y(NO3)3 solution (0.5M) was obtained by dissolving
micro-sized Y2O3 (99.999%) in water solution of HNO3. A
mixed solution of ethanol (20%) and ammonia with OHꢁ
concentration of 1.8M was used as precipitant. Before
injected into a reactor simultaneously at room temperature,
the Y(NO3)3 solution and the precipitant were stirred for an
hour separately by magnetic stirring. White slurry was
formed immediately under vigorous stirring. The pH value
was kept at around 9.0 by adjusting the flowing rate of
ammonia solution during the reaction process. The slurry
was filtered and washed repeatedly with deionized water,
and then distilled with n-butanol under reduced pressure.
The as-prepared precursors were calcined at 700 to 1100 ꢀC
for 2 h.
Jiangsu Province Cultivation base for State Key Laboratory of
Photovoltaic Science and Technology
Changzhou University
Changzhou, 213164 Jiangsu, China
E-mail: czh@cczu.edu.cn
Prof. W.-Q. Zhu
Suzhou Institute of Nano-Tech and Nano-bionics
Chinese Academy of Sciences
Suzhou, 215123 Jiangsu, China
Prof. J.-J. Xu
Dalian Maritime University
Dalian, Liaoning 116026, China
E-mail: jjxu@dlmu.edu.cn
DOI: 10.1002/pssa.201700417
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Figure 2. TEM morphology of Y2O3 nanopowders calcined at 900 ꢀC.
Figure 1. XRD patterns of the as prepared precursors calcined at 700 to
1100 ꢀC (b) for 2h.
well dispersed fine grains with particle size of about 20 nm in
average.
BaCO3 (99.9%), CaCO3 (99.9%), TiO2 (99.9%), SnO2 (99.5%),
and the as prepared Y2O3 nanopowders calcined at 900 ꢀC were
used as starting materials. According to the compositional
formula Ba0.90Ca0.10Ti0.90Sn0.10O3ꢁxY2O3 (x ¼ 0.0.09), the mate-
rials were mixed for 1h in ethanol medium, and then calcined at
1200 ꢀC for 4 h in air. The synthesized powders were dry pressed
into pellets with 8 wt.% polyvinyl alcohol (PVA) binder solution.
The pellets were sintered at 550 ꢀC for 2 h to remove the binder,
and then sintered at 1460 ꢀC for 2 h.
Figure 3 shows XRD patterns of the BCTSY ceramics
sintered at 1460 ꢀC for 2 h with different nano-Y2O3 content.
All the compositions show pure perovskite structure, indicating
Y3þ ions diffused into BCTS matrix. It is notable in the enlarged
patterns of (110) peak that the diffraction peaks shift toward
higher angle, which means the interplanar space of the
matrix crystal lattice changed[23] and the unit cell volume
shrank with the addition of Y3þ. Based on the ionic radius of
Ca2þ, Ba2þ, Sn4þ, and Ti4þ ion (0.100, 0.135, 0.071, and
0.068 nm respectively),[7,24] the unit cell volume shrinkage
should be ascribed from the occupation of the A site Ba2þ with
Y3þ (0.123 nm, CN ¼ 12).
Phase identification of the calcined Y2O3 powder and the
sintered products were analyzed using a diffractometer (Rigaku
̊
D/max-2500/PC, Japan, Cu K , λ ¼ 1.5406 A). The morphology
1
α
of the prepared nanopowders and the microstructure of the
ceramic samples were investigated via a TEM (JEM-2100) and a
scanning electron microscope (SEM, HITACHI S-4300),
respectively. The ceramic samples were thermally etched at
1150 ꢀC for 2 h before microstructure investigation. The sintered
pellets were polished to obtain flat and parallel surface, silver
paste was then fired on the surface as electrodes. Dielectric
properties were measured using the precision impedance
analyzer (4294 A Agilent Inc., Malaysia). The specimens were
polarized under an electric field of 3.5 kVmmꢁ1 in silicon oil at
room temperature, and the poled pellets were insulated for 2h at
every anneal temperature from 30 to 90 ꢀC. The corresponding
piezoelectric constant was measured by a quasi-static d33 meter
(ZJ-3AN, China).
Figure 4 presents SEM micrographs of the BCTSY ceramics.
The microstructure of pure BCST ceramic (x ¼ 0) is consists of
large grains with grain size above 100 μm and some small
grains. The grain sizes of the samples obviously decreased
with the addition of nano-Y2O3, showing the inhibition of
3. Results and Discussion
Figure 1 shows the X-ray diffraction patterns of the as-prepared
precursors calcined at 700 to 1100 ꢀC for 2 h. Characteristic
peaks of Y2O3 phase start to appear when calcined at 700 ꢀC,
indicating the as-precipitated powders remain amorphous till
this temperature. All the diffraction peaks correspond with the
JCPDS#83-0927, and become sharper with the increase of the
temperature. TEM morphology of Y2O3 nanoparticles calcined at
900 ꢀC is presented in Figure 2. The products are composed of
Figure 3. XRD patterns of the BCTSY ceramics sintered at 1460 ꢀC with
various Y2O3 content.
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56 ꢀC, and increase with further Ycontent. The
increase of TC in a certain range is often
associated with the reduction of the tolerance
factor (t) which reflects the degree of the
structural distortion.[26] The t value can be
calculated by the following formula:
RA þ RO
pffiffiffi
t ¼
2ðRB þ ROÞ
Where RA, RO, RB represent the ionic radius of
theA-site, B-site, andoxygenion, respectively.[27]
Apparently, the smaller Y3þ substitution in
Ba-site leads to a lower t value. However, large
local random electrical field and strain field in
the crystal lattice may work during the process,
which make TC shifts. The dielectric behavior
above TC/Tm is analyzed by the modified Curie-
γ
Weiss law, 1/ɛ– 1/ɛm ¼ (T-Tm) /C(T > Tm).[28]
The exponent γ reflects the nature of relaxor
phase transition, which can be calculated from
the data in Figure 7. The exponent takes values
in the range of 1.55–1.65 for all the samples
(shown in Figure 7), indicating a typical diffuse
phase transition characteristic.
Figure
8 illustrates the piezoelectric
coefficient d33 and planar mode electrome-
chanical coupling coefficient kp curves of the
BCTSY ceramics with different Y content. It
can be observed that the piezoelectric
property of the ceramics is obviously im-
proved at x ¼ 0.01, and then keeps decreas-
ing with further Y content. The maximum
Figure 4. SEM morphologies of the BCTSY ceramics with various Y2O3 content.
value of d33 and Kp is 596 pC/N and 57.1%,
respectively x ¼ 0.01, which is higher than
grain growth of the Y2O3. However such a pinning effect did not
lead to homogeneous microstructures, as some pores exist in the
grain or in the grain boundary, which may inevitably deteriorate
the electrical properties of the ceramics.
the micro-sized Y2O3 doped Ba(Ti0.96Sn0.04)O3 reported in
literature.[10] The improvement of the piezoelectric properties
is associated with the uniformly distributed microstructure
with certain amount of nano-sized Y2O3 doping. And the A site
substitution of Y3þ with donor doping effect may contribute to
the increase of the piezoelectric properties due to the ease of
dipole movement. The pinning effect in the grain boundary
with further Y2O3 addition makes the reorientation in small
Figure 5 shows the temperature dependences of er for the
BCTSY ceramics at 100 Hz, 1 kHz, 10 kHz, 100 kHz, and
500 kHz from 30 to 110 ꢀC. The peak value of dielectric constant
(emax) decreases with increasing frequency for each specimen,
meanwhile, TC keeps almost unchangeable, showing a fre-
quency dispersion behavior. Figure 6 shows the temperature
dependence of dielectric constant of the BCTSY ceramics at
1 kHz from 30 to 110 ꢀC. The inset shows the variation of emax
and TC as function of Y content. The nano-sized Y2O3 doping
apparently increases the emax value especially for the composi-
tion with x ¼ 0.01. By comparison, the dielectric constant of the
micro-sized Y2O3 doping Ba(Ti0.96Sn0.04)O3 ceramics reported in
literature is lower.[10] According to Jeong,[25] the vacancies
generated during the A-site substitution of Y3þ as donor in the
pervoskite structures can provide larger space, making strain
energy decreases during the domain rotation process. The
reduced energy consumption facilitates the movement of the
domains, thus contributes to the improvement of the dielectric
properties.[19] The TC peak fluctuates in a small range from 52 to
grains difficult, accordingly leads to the decrease of d33
.
Figure 9 shows the thermal stability of the BCTSY ceramics
at 30 to 90 ꢀC. The temperature stability was greatly improved
with increasing Y content. For the sample with x ¼ 0.07, the
change of d33 values is less than 6%. Moreover, the d33 values of
the sample with x ¼ 0.09 keep unchanged at 30 to 60 ꢀC,
exhibiting a weak temperature dependence behavior. Conse-
quently, the values of d33 of all the samples decrease at 60 to
90 ꢀC. It is notable that the declination temperature range is
broadened. The effect of Y3þ doping on the thermal depoling
behavior of the BCTS ceramics is the same with the Y doped
BCZT system.[9] As temperature dependence of the dielectric
and piezoelectric properties is always observed in the BaTiO3-
based ceramics due to the thermally activated reverse switching
of the non180ꢀ domain.[29]
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Figure 5. The temperature dependences of er for the BCTSY ceramics at 10, 1, 10, 100, and 500 kHz.
Figure 6. Temperature dependence of dielectric constant for the BCTSY
Figure 7. ln(1/e-1/em) versus ln(T-Tm) plots according to the temperature
ceramics at 1 kHz.
dependence of dielectric constant for BCTSY ceramics.
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CE20175041), and the Priority Academic Program Development of
Jiangsu Higher Education Institutions (Grant No. 15KJA43002).
Conflict of Interest
The authors declare no conflict of interest.
Keywords
BaTiO3, dielectrical properties, doping, Y2O3
Received: June 28, 2017
Revised: October 21, 2017
Published online:
Figure 8. Y content dependence on the d33 and kp of the BCTSY ceramics.
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4. Conclusions
Well dispersed Y2O3 nanopowders were prepared by the
azeotropic co-precipitation method. (Ba0.90Ca0.10)(Ti0.9Sn0.1
)
O3ꢁxY2O3 (BCTSY) lead-free piezoelectric ceramics doped
with the nano-sized Y2O3(x ¼ 0.01–0.09%) were synthesized at
1460 ꢀC by solid-state technique. All the BCTSYsamples possess
typical perovskite structure. Both of the piezoelectric and
dielectric properties of the samples were improved with nano-
Y2O3 addition. The maximum piezoelectric properties was
achieved with d33 of 596 pC/N and Kp of 57.1%, respectively at
x ¼ 0.01.
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The authors wish to acknowledge the financial support of National
Natural Science Foundation of China (Grant No. 51702024, 21403286);
Sci-Tech Support Plan-Social development of Changzhou City (Grant No.
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