Journal of Alloys and Compounds 794 (2019) 542e552

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Journal of Alloys and Compounds

journal homepage: http://www.elsevier.com/locate/jalcom

Enhanced piezoelectric response of (Ba,Ca)(Ti, Zr)O3 ceramics by super

large grain size and construction of phase boundary
Qianwei Zhang a, Wei Cai a, b, *, Qingting Li a, Rongli Gao a, b, Gang Chen a, b,
Xiaoling Deng a, b, Zhenhua Wang a, b, Xianlong Cao a, b, Chunlin Fu a, b, **
a
School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology, University Town, Shapingba District, Chongqing, 401331,
China
b
Chongqing Key Laboratory of Nano/Micro Composite Material and Device, University Town, Shapingba District, Chongqing, 401331, China

a r t i c l e i n f o a b s t r a c t

Article history: Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics with super large grain size (>50 mm) have been successfully
Received 18 February 2019 fabricated by sol-gel method. The effects of pH value of precursor solution on microstructure, electric
Received in revised form properties and fatigue behavior were systematically studied. BCZT ceramics with super large grain size
20 April 2019
(35e55 mm) were prepared by BCZT powders with large particle size (136e221 nm) by controlling the pH
Accepted 23 April 2019
Available online 25 April 2019
value. The grain size and densification of BCZT ceramics decrease with the increase of pH value of
precursor solution. XRD results indicate that there is the coexistence of rhombohedral and tetragonal
phase in BCZT ceramics synthesized by precursor solution with a pH of 3 and are the coexistence of
Keywords:
Sol-gel process
orthorhombic and tetragonal phase in BCZT ceramics synthesized by precursor solution with a pH of 5
Piezoelectric response and 7. BCZT ceramics shows obvious diffuse ferroelectric-paraelectric phase transition characteristic and
Ferroelectric properties the diffuseness behavior enhances as the pH value increases. The remnant polarization and coercive
(Ba, Ca)(Zr, Ti)O3 electric field of BCZT ceramics reduce with the decreased grain size caused by the increase of pH value.
The excellent piezoelectric properties (d33 ¼ 585.6 pC/N and d*33 ¼ 898 pm/V) of BCZT ceramics have been
obtained by super large grain size and the construction of phase boundary of tetragonal phase and
orthorhombic phase. Furthermore, BCZT ceramics with large grain size still has high fatigue resistance to
bipolar electric cycling.
© 2019 Elsevier B.V. All rights reserved.

1. Introduction comparable to PZT ceramics [3,4]. To find out lead-free piezocer-

amics candidates, various materials system such as BaTiO3 [5,6],
Lead-based piezoelectric materials such as Pb(Zr,Ti)O3 (PZT, (Bi,Na)TiO3 [7,8] and (K,Na)NbO3 [9,10] based ceramics have been
d33~600 pC/N) and related materials are used extensively for a va- extensively studied. Among lead-free piezoceramics, BaTiO3-based
riety of devices (actuator, sensor and ultrasonic transducers et al.) ceramics with ABO3 perovskite structure in which Ba2þ at A sites is
on account of their excellent piezoelectric properties [1,2]. But partially substituted by divalent metal ions and Ti4þ at B sites by
there are serious environmental problems in synthesis and waste tetravalent metal ions have attracted much attention [11,12]. Ren
treatment processes of lead-based piezoelectric materials. There- et al. found that Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) piezoceramics have
fore, lead-free piezoelectric materials have become a hotspot due to high piezoelectric coefficient (d33 ¼ 550e620 pC/N), which is
their non-toxicity and excellent piezoelectric properties caused by the existence of tripe-point type morphotropic phase
boundary [13].
For further improving piezoelectric properties, the optimization
of synthesis and sintering conditions [14e16], texture [17,18] and
* Corresponding author. School of Metallurgy and Materials Engineering,
doping (such as Nd3þ, Y3þ, Gd3þ, Tb3þ, Mn2þ, Sn4þ et al.) [19e23] of
Chongqing University of Science and Technology, University Town, Shapingba
District, Chongqing, 401331, China. BCZT ceramics have been performed. In fact, it is not easy to achieve
** Corresponding author. School of Metallurgy and Materials Engineering, d33 value above 500 pC/N of BCZT piezoceramics except for appli-
Chongqing University of Science and Technology, University Town, Shapingba cation of texture. An important reason for not obtaining the high
District, Chongqing, 401331, China. piezoelectric coefficient d33 may be due to the synthesis method of
E-mail addresses: caiwei_cqu@163.com (W. Cai), chlfu@126.com (C. Fu).

https://doi.org/10.1016/j.jallcom.2019.04.247
0925-8388/© 2019 Elsevier B.V. All rights reserved.
 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552 543

powders. The methods of piezoceramics such as solid-state reac- 2. Experimental details

tion method are difficult to make its compositions homogeneous
distribution. Compared to solid-state reaction method, soft- 2.1. Preparation
chemical routes such as sol-gel [24,25], hydrothermal [26], sol-gel
auto combustion [27,28] and oxalate precursor coprecipitation Ba0.85Ca0.15Zr0.1Ti0.9O3 powders were synthesized by sol-gel
[29] method have shown remarkable advantages such as compo- method. Fig. 1 shows the process flow chart of the preparation for
sitional homogeneity, accurate stoichiometric ratio and lower BCZT powders. Barium acetate (Ba(CH3COO)2, 99%, Sinopharm
crystallization temperature because of the mixing of liquid pre- Group Co. Ltd.), calcium acetate (Ca(CH3COO)2$H2O, 99%), zirco-
cursors on the molecular level. In general, sol-gel method is nium n-butoxide (ZrO4C16H36, 99%) and tetrabutyl titanate
beneficial to obtain BCZT nanopowders, which is caused by the (Ti(OC4H9)4, 99.5%) were used as starting materials. Firstly, barium
reduction of sintering temperature and powder agglomeration. acetate and calcium acetate were weighed and dissolved in acetic
And BCZT ceramics with small grain size can be fabricated at lower acid solution as solvents, and then continuously stirred in water
sintering temperature by BCZT nanopowders with high sintering bath (80  C) to form a transparent and homogenous precursor so-
activity. Yang et al. prepared Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics with lution of Ba2þ and Ca2þ. Secondly, zirconium n-butoxide and tet-
small grain size by optimizing process parameters such as bathing rabutyl titanate were weighed in stoichiometric proportions and
temperature and the concentration of acetic acid and Ti precursor dissolved in 2-ethoxyethanol as solvents (the volume ratio of tet-
solution of sol-gel method and found that BCZT ceramics prepared rabutyl titanate to 2-ethoxyethanol was 3:8) and continuously
by sol-gel method exhibited more excellent electric properties stirred in water bath (80  C) to obtain a precursor solution of Zr4þ
(d33 ¼ 558 pC/N, Pr ¼ 12.15 mC/cm2 and Ec ¼ 1.78 kV/cm) than that of and Ti4þ. To control the hydrolysis rate of tetrabutyl titanate, a
the ceramic samples fabricated by solid-state method [30]. Das certain amount of acetylacetone (the volume ratio of acetylacetone
et al. prepared Ba0.85Ca0.15Zr0.1Ti0.9O3 nanoparticles (<50 nm) via to 2-ethoxyethanol was 1:8) was added as a chelating agent into
sol-gel method and then obtained BCZT ceramics with high dense the precursor solution of Zr4þ and Ti4þ. Thirdly, the precursor so-
(95% of the theoretical density) and homogeneous microstructure lution of Zr4þ and Ti4þ were added dropwise to the precursor so-
and moderate grain size (10e20 mm) by solid-state sintering, and lution of Ba2þ and Ca2þ and continuously stirred at 80  C to form
BCZT ceramics show outstanding piezoelectric properties the mixed solution. The pH value of the mixed solution was
(d33 ¼ 558 pC/N, dynamic piezoelectric coefficient d*33~942 p.m./V, controlled to 3, 5 and 7 respectively by adding different amounts of
electromechanical coupling coefficient kp~ 0.45) comparable to NH4OH and then continuously stirred at 80  C to obtain apparent
lead-based piezoceramics [31]. The similar results were reported by sol. The sol was aged at room temperature (25  C) for 24 h and then
Zhang et al. [24]. As everyone knows, the grain size of piezoelectric dried at 120  C to form dry gels. Finally, BCZT powders were ob-
ceramics has significant effects on its electric properties and the tained by calcining dry gels at 1000  C for 2 h.
larger grain size is favorable to obtain enhanced ferroelectric and BCZT powders prepared by precursor solution with different pH
piezoelectric properties [29,32e35]. There has been some research values (3, 5 and 7) were mixed with 15 wt% binder (polyvinyl
on the influences of grain size on piezoelectric response of BCZT alcohol) and then pressed into green pellets with a diameter of
ceramics. Hao et al. fabricated BCZT ceramics with the grain size of 10 mm and thickness of 1 mm at 15 MPa pressure. To obtain BCZT
0.4e32.2 mm by different methods and found that BCZT ceramics ceramics with super grain size, the pellets were sintered at 1530  C
exhibited excellent piezoelectric properties (d33 > 470 pC/N, for 10 h in air. BCZT ceramics prepared by precursor solution with a
d*33>950 p.m./V and kp > 0.48) when the grain size is beyond 10 mm pH of 3, 5 and 7 are represented as BCZT-3, BCZT-5 and BCZT-7
[32]. Lin et al. prepared BCZT ceramics with the grain size of respectively.
6.51e20.57 mm and found that the best piezoelectric properties
(d33~ 416 pC/N and kp~0.558) result from the largest grain size [33]. 2.2. Characterization
Maca et al. prepared BCZT ceramics with the grain size of
16.5e44.5 mm and found that the enhanced piezoelectric properties The XRD patterns of BCZT powders and BCZT ceramics were
(d33 ¼ 470e480 pC/N) was obtained when the grain size is obtained by X-ray diffraction (XRD, SmartLab-9, Rigaku, 40 kV,
10e20 mm, and the highest remnant polarization (Pr  12 mC/cm2) 30 mA, Japan) with Cu Ka radiation. The density of ceramic samples
was obtained when the grain size is 25e45 mm [34]. Hou et al. was determined by Archimedes' principle. The surface morphol-
prepared Ba0.85Ca0.15Zr0.1Ti0.9O3 with the grain size of 10e15 mm ogies of BCZT powders and BCZT ceramics were carried out using a
and found that d33 is the maximum (~530 pC/N) when the grain
size is 13.7 mm, which results from the enhanced remnant polari-
zation and reduced coercive electric field [35]. In summary, the
grain size has significant impacts on the piezoelectric response of
BCZT ceramics. Large and uniform grain of BCZT ceramics may be
beneficial to obtain excellent piezoelectric properties. However,
there is no report on the effects of super large grain size (>50 mm)
on the electric properties of BCZT ceramics. Sol-gel method is a
typical route to fabricate BCZT piezoceramics with uniform grain
and the pH value of precursor solution has significant effects on the
grain size of BCZT ceramics because of significantly influencing the
particle size of powders [24,25,27,28]. For this purpose, we have
made attempts to fabricate BCZT ceramics with super large and
uniform grains via sol-gel method. In this work, BCZT ceramics with
super large and uniform grains have been synthesized via sol-gel
method and a systematic research on the effects of pH value of
precursor solution on microstructure, dielectric, ferroelectric and
piezoelectric properties and bipolar fatigue behavior was carried
out. Fig. 1. The synthesis process of BCZT powders by sol-gel method.
544 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552

field emission scanning electron microscope (FESEM, JSM-7800F, fitting results of diffraction peaks around 45 (Fig. 2(c)), it is
JEOL, Japan) and scanning electron microscopy (SEM, S-3700 N, concluded that BCZT-3 ceramics is the coexistence of R and T phase,
Hitachi, Japan) respectively. The dielectric constant and loss of BCZT and BCZT-5 and BCZT-7 ceramics are the coexistence of O and T
ceramics as a function of temperature in a range of 25e200  C with phase, which suggests that the pH value of precursor solution (to
1  C/min were obtained by an LCR meter (LCR, HP 4980A, Agilent, avoid duplication, “the pH value of precursor solution” is abbrevi-
USA). The ferroelectric hysteresis loops and strain-electric field (S- ated as “pH value”) has obvious impacts on the construction of
E) loops of BCZT ceramics were determined by ferroelectric test phase boundary of BCZT ceramics. It is also found that the intensity
system (TF2000E, aixACCT, Germany) connected with a laser of diffraction peaks around 45 of BCZT-5 ceramics corresponding
interferometer vibrometer (SP-S 120/500, SIOS Mebtechnik GmbH, to (002)/(200) is apparently higher than that of BCZT-3 and BCZT-7
llmenau, Germany). After the poling of the ceramic samples at 60  C ceramics, indicating that BCZT-5 ceramics show (001) orientation
in a silicone oil bath by applying a DC field of 10 kV/cm for 20 min, characteristic. But the reason of orientation is not clear. Moreover,
the quasi-static piezoelectric coefficient d33 was determined by a the lattice constants of BCZT ceramics were obtained by Bragg
quasi-static d33 meter (ZJ-4, Chinese Academy of Sciences, China). equation (2dsinq ¼ nl) and shown in Table 1. It is seen that the
The study of fatigue behavior was performed on unpoled BCZT tetragonality (c/a) of BCZT ceramics slightly increases with the in-
ceramics by applying a 10 Hz bipolar triangular waveform at 10 kV/ crease of pH value.
cm (3e4 times coercive electric field (EC)) for 106 cycles. To reveal the effects of pH value on the particle size and dis-
persibility of BCZT powders, FESEM images were shown in Fig. 3.
The average particle size of BCZT powders prepared by a pH of 3, 5
3. Results and discussion and 7 is 221 nm, 205 nm and 136 nm respectively, indicating that
BCZT powders become finer as the pH value increases. It is similar
3.1. Microstructure to the results calculated by the Scherrer equation. It is worthwhile
to note that the particle size of our BCZT powders is obviously larger
The XRD patterns of BCZT powders and BCZT ceramics are than that of the powders reported in literature [31,36], which is
shown in Fig. 2. According to XRD patterns of BCZT powders beneficial to the preparation of BCZT ceramics with super large
(Fig. 2(a)), BCZT powders prepared by the precursor solution with a grain size. Furthermore, compared with the BCZT powder prepared
pH of 3e7 show pure phase with perovskite structure and the by precursor solution with a pH of 3 and 5, BCZT powders prepared
impurity phase is not observed. It is well known that the crystallite by precursor solution with a pH of 7 has better dispersibility. In a
size can be obtained by the Scherrer equation (1): word, the neutral precursor solution (pH ¼ 7) for BCZT powder in
sol-gel process is beneficial to gain finer particle with better dis-
Kl persibility. Predictably, BCZT ceramics prepared by our BCZT pow-
D¼ (1)
b sin q der with larger particle size should have larger grain size.
To find out the effects of pH value on densification and grain
where D is crystallite size (nm), K is the shape factor, b is full width size, the images of SEM and grain size distribution of BCZT ceramics
of the diffraction peak at half maximum, l is the wavelength of X- are given in Fig. 4. Firstly, BCZT-3 and BCZT-5 ceramics show dense
rays. The crystallite size of BCZT powders prepared by precursor and crack-free surface, and there are some pores in BCZT-7
solution with a pH of 3, 5 and 7 calculated by Eq. (1) is 204 nm,
177 nm and 119 nm respectively, which indicates that BCZT pow-
ders becomes finer as the pH value increases.
Table 1
According to Fig. 2(b), it is seen that BCZT ceramics fabricated by Lattice constants of BCZT ceramics prepared by precursor solution with different pH
precursor solution with a pH of 3, 5 and 7 show pure phase with values.
perovskite structure. To find out the phase evolution, fine scanning
Sample Lattice parameters Tetragonality
in the range of 45e46 was carried out (Fig. 2(c)) and the diffraction
a (nm) c (nm) c/a
peaks were fitted by Gaussian profile. In general, the diffraction
peaks of BaTiO3 around 45 may correspond to (002)/(200)T of the BCZT-3 0.3991 0.4002 1.0027
tetragonal phase (T), (200)R of the rhombohedral phase (R) and BCZT-5 0.3985 0.4000 1.0037
BCZT-7 0.3984 0.4005 1.0052
(200)/(220)O of the orthorhombic phase (O) [16]. According to the

Fig. 2. XRD patterns of (a) BCZT powders and (b) BCZT ceramics (c) XRD patterns around 45  2q  46 of BCZT ceramics.
 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552 545

Fig. 3. The FESEM images of BCZT powders prepared by precursor solution with different pH values (a) pH ¼ 3, (b) pH ¼ 5 and (c) pH ¼ 7.

Fig. 4. The images of SEM and grain size distribution of BCZT ceramics (a)(d) BCZT-3, (b)(e) BCZT-5 and (c)(f) BCZT-7.

ceramics. The relative density of BCZT-3, BCZT-5 and BCZT-7 ce- respectively. The results indicate that the lower pH value is favor-
ramics obtained by Archimedes method is 96.7%, 95.8% and 91.5% able to obtain good densification of BCZT ceramics. The
546 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552

densification of BCZT-7 ceramics is not good, which may be due to increases as temperature rises when temperature is above 180  C,
that the sintering temperature (1530  C) is too high for BCZT-7 which is caused by the enhanced mobility of carrier such as elec-
ceramics prepared by BCZT powder with smaller particle size and tron and hole in the higher temperature.
leads to recrystallization [37]. Secondly, the average grain size (Ga) To compare the dielectric properties of BCZT-3, BCZT-5 and
and grain size distribution of BCZT ceramics obtained by Nano BCZT-7 ceramics, the temperature dependences of dielectric con-
Measurer software are given in Fig. 4(d), (e) and (f). The average stant and loss measured at 1 kHz are given in Fig. 6. Firstly, the Curie
grain size of BCZT-3, BCZT-5 and BCZT-7 ceramics is 55 mm, 50 mm temperature (TC) of BCZT-3, BCZT-5 and BCZT-7 ceramics is 90  C,
and 35 mm respectively, which suggests that the average grain size 91  C and 94.9  C respectively, indicating that the Curie tempera-
decreases as the pH value increases. The result is consistent with ture increases as the pH value increases. It is also seen that the O-T
the pH value dependence of particle size of BCZT powders. More- or R-T phase transition temperature (TO-T or TR-T) of BCZT ceramics
over, the grain uniformity of BCZT-5 ceramics is superior to that of shifts to higher temperature as the pH value increases. As shown
BCZT-3 and BCZT-7 ceramics (see Fig. 4(d), (e) and (f)). previously, the grain size of BCZT ceramics decreases with the in-
crease of the pH value. In other words, TC and TO-T or TR-T of BCZT
ceramics increase as its grain size decreases. The result is consistent
3.2. Dielectric properties
with Zhai's result [32] and different from the other reports [41,42].
Frey [41] and Martirena [42] et al. proposed that TC shifts to lower
Fig. 5 shows the dielectric constant and dielectric loss as a
function of temperature measured at various frequencies with the
step scan of 1  C/min in BCZT ceramics. Firstly, all BCZT ceramics
show two distinct peaks of dielectric constant in the range of
25e200  C, indicating that there are two phase transition. These
two peaks of dielectric constant correspond to the phase transition
of O-T phase (TO-T) or R-T (TR-T) phase around 30e60  C and T-C (TT-

C) phase near 90 C respectively, which is consistent with the
coexistence of rhombohedral-tetragonal phase for BCZT-3 ceramics
and orthorhombic-tetragonal phase for BCZT-5 and BCZT-7 ce-
ramics obtained by XRD patterns [34]. The result is similar to the
literature [16,38,39]. Secondly, the Curie temperature (TC) (tetrag-
onal-cubic phase transition temperature) of all BCZT ceramics re-
mains unchanged as the frequency increases, indicating that there
is no obvious frequency dispersion phenomenon. Thirdly, the
maximum dielectric constant of all BCZT ceramics decreases
slightly as frequency increases, which result from the relaxation of
different polarization mechanisms (ionic, dipole and space-charge
polarization) [40]. In addition, the dielectric loss of all BCZT ce- Fig. 6. The temperature dependences of dielectric constant and dielectric loss of BCZT
ramics decreases slightly with the increase of frequency, and ceramics.

Fig. 5. The dielectric constant and dielectric loss as a function of temperature of BCZT ceramics (a) BCZT-3, (b) BCZT-5 and (c) BCZT-7.
 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552 547

temperature regions owing to the emergence of the higher internal several methods have been used in the following [47]. As everyone
stress in fine-grained piezoceramics, and BaTiO3-based ceramics knows, the dielectric constant of a normal ferroelectric follows
with fine grain have higher internal stress because of the absence of Curie-Weiss law above the Curie temperature, as follow:
90 ferroelectric domain walls. Based on the same stress model
[43], TC of BCZT ceramics should also shift to lower temperature as 1 T  T0
¼ ðT > T0 Þ (2)
the grain size decreases. However, the variation of TC with the grain εr C
size in our BCZT ceramics show the opposite trend. It may be due to
that the stress model is not applicable to BCZT ceramics with super where C is Curie-Weiss constant and T0 is Curie-Weiss temperature.
large grain size. Besides grain size, the tetragonality (c/a) of BaTiO3- Fig. 7 illustrates the plots of the inverse dielectric constant versus
based materials is the other important factor influencing TC. temperature in BCZT ceramics measured at 1 kHz. By linear
Generally speaking, the Curie temperature of BaTiO3-based mate- extrapolating of inverse dielectric constant in the high-temperature
rials increases with the increase of its tetragonality [44]. The tet- region, T0 and C are obtained by Eq. (2). The result suggests that the
ragonality of our BCZT ceramics increases as the pH value increases dielectric constant of all samples deviate from the Curie-Weiss law.
(shown in Table 1), which leads to the increase of TC. Secondly, the The degree of the deviation from the Curie-Weiss law is repre-
maximum dielectric constant of BCZT-3, BCZT-5 and BCZT-7 ce- sented by DTm described as follows:
ramics is 25334, 27038 and 18813 respectively and the room-
temperature (25  C) dielectric constant of BCZT-3, BCZT-5 and DTm ¼ TCW  Tm (3)
BCZT-7 ceramics is 4551, 4583 and 2571 respectively. The
maximum dielectric constant of BCZT-7 ceramics is obviously lower where TCW is the temperature of deviating the Curie-Weiss law and
than that of BCZT-3 and BCZT-5 ceramics, which is due to the effect Tm is the temperature corresponding to the maximum dielectric
of grain size. The average grain size (35 mm) of BCZT-7 ceramics is constant. All obtained parameters by Eq. (2) and Eq. (3) are given in
the smallest in all ceramic samples. It is generally known that the Table 2. It is seen that DTm of BCZT ceramics increase with the in-
dielectric constant of ferroelectric materials decreases with grain crease of pH value, indicating the enhancement of diffuseness
refinement, which is due to that the contribution of grain to po- behavior of BCZT ceramics.
larization of ferroelectric materials is greater than that of grain To further confirm the diffuseness, a modified form of Curie-
boundary [45]. Thirdly, the dielectric loss of BCZT ceramics slightly Weiss law was proposed as follows:
increases as pH value increases when temperature is below 120  C.
Moreover, there is broadening of the maximum dielectric constant 1 1 ðT  Tm Þg
 ¼ 0 (5)
peak of all BCZT ceramics, which indicates that BCZT ceramics have εr εm C
diffuse phase transition characteristic. It is associated to structural 0

disorder and compositional fluctuations in BCZT ceramics [46]. where g and C are constant, εm and Tm are the maximum dielectric
To further characterize the diffuseness of phase transition, constant and its corresponding temperature. The diffuseness con-
stant g (1  g  2) represents the character of the phase transition.

Fig. 7. The plots of inverse dielectric constant versus temperature in BCZT ceramics (a) BCZT-3, (b) BCZT-5 and (c) BCZT-7.
548 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552

Table 2 of BCZT ceramics measured at 10 Hz. The remnant polarization

The Curie-Weiss temperature (T0), the Curie-Weiss constant (C), TCW and DTm of (2Pr), saturation polarization (2Ps) and the coercive electric field
BCZT ceramics.
(2Ec) are obtained and given in Table 3. Firstly, the well saturated
Sample BCZT-3 BCZT-5 BCZT-7 hysteresis loops confirm the excellent ferroelectricity of BCZT ce-
T0 ( C) 115.51 117.65 118.64 ramics. The high remnant polarization (2Pr > 26 mC/cm2) of BCZT-3
Tm ( C) 90 91.1 94.9 and BCZT-5 ceramics with large grain size (50e55 mm) are obtained
C (  105 K) 1.546 1.62 1.415 under lower electric field (10 kV/cm) and the remnant polarization
TCW ( C) 167 169 173
of BCZT-7 ceramics with relatively small grain size (35 mm) de-
DTm ( C) 77 77.9 78.1
creases obviously, which indicates that the remnant polarization of
BCZT ceramics increases with the increase of grain size. This is
mainly due to two reasons. On the one hand, the proportion (f) of
g ¼ 1 and g ¼ 2 represent normal ferroelectric-paraelectric phase grains contribution to polarization for ferroelectric materials can be
transition in accord with Curie-Weiss law and a complete diffuse
described by f ¼ f0[1-exp(-Gad3/kT)], where d is the grain size, and
phase transition respectively. The plots of ln(1/εr 1/εm)-ln(T-Tm) of
Ga is a constant and represents the grain anisotropy energy density
BCZT ceramics are given in Fig. 8. The plots show obvious linear
[32,48]. The proportion (f) of grains contribution is only related to
characteristics. According to Eq. (5), the slope of the linear fitting
the grain size (d). Thus, the contribution of grain to polarization
line is the diffuseness constant g. The diffuseness constant g in-
increases with the increase of grain size, which leads to the
creases from 1.54 to 1.58 with the increase of pH value, indicating
enhancement of ferroelectricity. On the other hand, as we all know,
the enhancement of diffuse phase transition. In general, the
it is difficult to form large ferroelectric domain in small grain, which
diffuseness of phase transition in ferroelectric materials enhances
results in reduced effective contribution to total polarization of
as grain size decreases [15]. As shown previously, the grain size of
ferroelectric materials [49]. Secondly, there are two obvious current
BCZT ceramics decreases with the increase of pH value and results
peaks in I-E loops of BCZT ceramics, which result from the
in the enhancement of diffuse phase transition. It is worth noting
switching of ferroelectric domain. The coercive electric field (2Ec) of
that the diffuseness constant g (1.54e1.58) of our BCZT ceramics is
BCZT ceramics is lower (2.74e3.22 kV/cm) and slightly decreases
lower than that (g ¼ 1.65e1.9) of BCZT ceramics reported in the
with the increase of pH value. In other words, the coercive electric
literature [15,24]. This is due to that the grain size of our BCZT ce-
field decreases as the grain size of BCZT ceramics reduces. The result
ramics is obviously larger than that of the samples reported in the
is different from the literature [50]. In general, the large grain of
literature.
ferroelectric ceramics is beneficial to switching of ferroelectric
domain and results in reduced coercive electric field [50]. Our
opposite result may be related to the effects of porosity on coercive
3.3. Ferroelectric properties
electric field. The reduced internal stress near the pores facilitates
the ease of domain switching in ferroelectric ceramics [34,51]. As
Fig. 9 shows the hysteresis loops and current-electric field loops

Fig. 8. Plots of ln(1/ε-1/εm)-ln(T-Tm) of BCZT ceramics (a) BCZT-3, (b) BCZT-5 and (c) BCZT-7.
 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552 549

Fig. 9. P-E and I-E curves of BCZT ceramics (a) BCZT-3, (b) BCZT-5 and (c) BCZT-7.

Table 3
The remnant polarization(2Pr), saturation polarization (2Ps) and coercive electric
field (2Ec) of BCZT ceramics.

Sample BCZT-3 BCZT-5 BCZT-7

2Pr (mC/cm2) 27.12 26.63 19.61

2Ps (mC/cm2) 39.54 34.34 28.28
2Ec (kV/cm) 3.22 2.84 2.74

mentioned above, the densification of BCZT-3, BCZT-5 and BCZT-7

ceramics gradually decreases. In other words, the porosity of
BCZT-3, BCZT-5 and BCZT-7 ceramics gradually increases.

3.4. Piezoelectric properties

A Berlincourt-type quasi-static d33 meter and ferroelectric test

system were applied to measure the piezoelectric coefficient d33
Fig. 10. Electric field-induced strain loops and dynamic piezoelectric coefficient of
and electric field-induced strain (S) curves of BCZT ceramics. Fig. 10
BCZT ceramics.
shows the electric field dependences of strain and dynamic
piezoelectric coefficient (d*33 ¼ Smax/Emax, also known as converse
piezoelectric coefficient) of BCZT ceramics measured at 10 Hz.
Firstly, the electric field-induced strain curves of all BCZT ceramics that of BCZT ceramics reported in the literature [54,55]. Secondly,
show typical “butterfly” characteristics. Because the well saturated the dynamic piezoelectric coefficient d*33 of BCZT ceramics was
P-E hysteresis loops of our BCZT ceramics can be obtained under obtained by the butterfly curves. The dynamic piezoelectric coef-
lower electric field, the strain-electric field curves were also ficient d*33 of BCZT-3, BCZT-5 and BCZT-7 ceramics is 768 pm/V, 898
measured under the same electric field (10 kV/cm). The maximum pm/V and 523 pm/V respectively, which suggests that BCZT-5 ce-
electric field-induced strain of BCZT-3, BCZT-5 and BCZT-7 ceramics ramics have the best piezoelectric properties. Thirdly, the quasi-
is 0.10%, 0.11% and 0.06% respectively, which indicates that the static piezoelectric coefficient (d33) of BCZT-3, BCZT-5 and BCZT-7
piezoelectric response of BCZT-5 ceramics is the highest. Although ceramics is 532.8 pC/N, 585.6 pC/N and 328.1 pC/N respectively
the maximum electric field-induced strain of our BCZT ceramics is (shown in Fig. 11), which further confirms that the piezoelectric
slightly lower than that of BCZT ceramics measured under higher properties of BCZT-5 ceramics is the best. In general, the piezo-
electric field reported in the literature [32,52,53], the electric field- electric properties of BCZT ceramics are significantly affected by the
induced strain of our BCZT ceramics (especially BCZT-3 and BCZT-5) grain size and enhances with the increase of grain size [15]. The
measured under the same electric field (10 kV/cm) is higher than grain size of BCZT-3 ceramics is the maximum in all ceramic
550 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552

with more switchable polarization directions and non-180 domain

walls is higher than that of BCZT-3 ceramics with less switchable
polarization directions and non-180 domain walls. Furthermore,
BCZT-7 ceramics with the coexistence of O and T phase have more
switchable polarization directions and non-180 domain walls, but
its density and grain size are the least in all ceramic samples, which
results in relatively lower piezoelectric coefficient. In summary, the
excellent piezoelectric response (d33 ¼ 585.6 pC/N and d*33 ¼ 898
pm/V) of BCZT-5 ceramics can be related to the construction of
phase boundary of tetragonal and orthorhombic phase and low
coercive electric field caused by super large grain size, which is very
attractive for actuator applications.

3.5. Fatigue behavior

Fig. 11. The quasi-static piezoelectric coefficient and dynamic piezoelectric coefficient Piezoelectric ceramics are often used in multiple field environ-
of BCZT ceramics.
ments (electric field-force field-temperature field). Therefore, the
fatigue behavior of piezoelectric ceramics is the focus of attention
[58]. To find out the evolution of fatigue behavior, the P-E hysteresis
samples, but its piezoelectric coefficient is not the maximum. The
loops before and after 106 bipolar triangular waveform cycles and
result suggests that the grain size is not the only influencing factor
the variations of remnant polarization (Pþ 
r and Pr ), saturated po-
of piezoelectric coefficient of BCZT ceramics. The number of avail-
larization (Ps and Ps ), coercive electric field (Ec and E
þ  þ
c ) and the
able polarization direction and domain structure are the other
Eþ þE
important factors influencing piezoelectric properties of BCZT ce- internal bias field (Eib, Eib ¼  c 2 c ) with cycle number of BCZT
ramics. The more switchable polarization directions in BCZT ma- ceramics are given in Fig. 12. Firstly, the hysteresis loops of all BCZT
terials can lead to the better piezoelectric property. There are eight ceramics after 106 cycles under 10 kV/cm still show sharp corners
available polarization directions for rhombohedral phase and six (shown in Fig. 12(a), (b) and (c)), which suggests that there are no
available polarization directions for tetragonal phase, but twelve significant increase in the electric conduction during fatigue [59].
available polarization directions for the orthorhombic phase in All BCZT ceramics exhibited a decrease in the saturated polarization
perovskite piezoelectric materials [56]. Moreover, there are 180 , and remnant polarization after 106 cycles. The remnant polariza-
90 , 60 and 120 domains in orthorhombic phase, and there are tion (Pþ 
r and Pr ) of all BCZT ceramics remains constant up to 10
3

180 , 71 and 109 domains in rhombohedral phase. The presence cycles, but Pþ
r and P 
r of BCZT-3, BCZT-5 and BCZT-7 ceramics de-
of non-180 domain walls will benefit the piezoelectric properties creases by 19.6% and 21.5%, 18.9% and 21.5%, 13.7% and 13.3%
as a result of the flattened energy profiles [57]. The number of non- respectively after 106 cycles. It is worthy to point out that bipolar
180 domain walls in orthorhombic phase is more than that of non- electric cycling has a more severe effect on the degradation of
180 domain walls in rhombohedral phase. According to above electric properties than unipolar cycling [60] and the magnitude of
mentioned XRD results, BCZT-3 ceramics is the coexistence of R and the maximum electric field and cycling frequency are important
T phase, and BCZT-5 and BCZT-7 ceramics are the coexistence of O factors influencing bipolar fatigue behavior [61]. The external
and T phase. Thus, the piezoelectric coefficient of BCZT-5 ceramics electric field can make the domain wall move, and the ferroelectric

Fig. 12. The P-E hysteresis loops of (a) BCZT-3, (b) BCZT-5 and (c) BCZT-7 ceramics at 10 kV/cm and 10 Hz and the variations of remnant polarization, saturated polarization, coercive
electric field and the internal bias field of (d) BCZT-3 (e) BCZT-5 and (f) BCZT-7 ceramics before and after 106 cycles of cycling at 10 Hz.
 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552 551

materials experience severe fatigue degradation when dipoles are Talents of Scientific and Technological Innovation in Chongqing, the
fully switched by electric field during every electric field reversal Chongqing Research Program of Basic Research and Frontier
(especially Emax [ Ec) [62]. The lower cycling frequency makes Technology (Grant No. CSTC2018jcyjAX0416, CSTC2016jcyjA0175,
dipoles have more time to switch under electric field and results in CSTC2016jcyjA0349) and the Innovative Entrepreneurship Training
an earlier degradation than higher cycling frequency [63,64]. Program for College Students in Chongqing (201811551013).
Compared to the other literature [65e67], the higher external
electric field (10 kV/cm, approximately 3e4 times the coercive
electric field) and relatively low cycling frequency (10 Hz) were References
applied in our fatigue test for BCZT ceramics. The result indicates [1] J.G. Hao, W. Li, J.W. Zhai, H. Chen, Progress in high-strain perovskite piezo-
that our BCZT ceramics experience less depolarization during bi- electric ceramics, Mater. Sci. Eng. R. 135 (2019) 1e57.
polar electric cycling and are superior to PZT ceramics. According to [2] X.Y. Gao, J.G. Wu, Y. Yu, Z.Q. Chu, H.D. Shi, S.X. Dong, Giant piezoelectric co-
efficients in relaxor piezoelectric ceramic PNN-PZT for vibration energy har-
the literature [68], PZT ceramics with large grain size show more
vesting, Adv. Funct. Mater. 28 (2018) 1706895.
severe degradation of property during electric cycling compared to [3] K.J. Shibata, R.P. Wang, T.S.K. Tou, J. Koruza, Applications of lead-free piezo-
the ceramic samples with small grain size. The fatigue resistance of electric materials, MRS Bull. 43 (2018) 612e616.
BCZT-3, BCZT-5 and BCZT-7 ceramics gradually becomes better, [4] T. Zheng, J.G. Wu, D.Q. Xiao, J.G. Zhu, Recent development in lead-free
perovskite piezoelectric bulk materials, Prog. Mater. Sci. 98 (2018) 552e624.
which is consistent with the effects of grain size on fatigue [5] J.H. Gao, D.Z. Xue, W.F. Liu, C. Zhou, X.B. Ren, Recent progress on BaTiO3-based
behavior. Even for BCZT-3 ceramics with super large grain size piezoelectric ceramics for actuator applications, Actuators 6 (2017) 24e44.
(55 mm), the ceramic sample still has high fatigue resistance to bi- [6] M.S. Alkathy, K.C.J. Raju, Structural, dielectric, electromechanical, piezoelec-
tric, elastic and ferroelectric properties of lanthanum and sodium co-
polar electric cycling. Moreover, Pþ 
r and Pr of BCZT ceramics are substituted barium titanate ceramics, J. Alloys Compd. 737 (2018) 464e476.
asymmetrical and the degree of positive and negative aging is [7] T.Y. Li, X.J. Lou, X.Q. Ke, S.D. Cheng, S.B. Mi, X.J. Wang, J. Shi, X. Liu, G.Z. Dong,
inconsistent, which may result from internal bias field [69,70]. H.Q. Fan, Y.Z. Wang, X.L. Tan, Giant strain with low hysteresis in A-site-defi-
cient (Bi0.5Na0.5)TiO3-based lead-free piezoceramics, Acta Mater. 128 (2017)
Secondly, Eþ 
c and Ec of all BCZT ceramics remain constant up to 10
3
337e344.
cycles, but Eþ
c and E 
c of BCZT-3 and BCZT-5 ceramics increases by [8] J. Yin, C.L. Zhao, Y.X. Zhang, J.G. Wu, Ultrahigh strain in site engineering-
20.6% and 23.8%, 29.9% and 34.8% respectively, and Eþ 
c and Ec of independent Bi0.5Na0.5TiO3-based relaxor-ferroelectrics, Acta Mater. 147
(2018) 70e77.
BCZT-7 ceramics decreases by 8.5% and 8.3% after 106 cycles, which [9] K. Wang, F.Z. Yao, J. Koruza, L.Q. Cheng, F.H. Schader, M.H. Zhang, J. Ro €del,
further confirms that there are obvious internal bias field in BCZT-3 J.F. Li, K.G. Webber, Electromechanical properties of CaZrO3 modified (K,Na)
and BCZT-5 ceramics. The internal bias field results from the NbO3-based lead-free piezoceramics under uniaxial stress conditions, J. Am.
Ceram. Soc. 100 (2017) 2116e2122.
domain walls pinned by the oxygen vacancies in BCZT ceramics
[10] P. Li, X.Q. Chen, F.F. Wang, B. Shen, J.W. Zhai, S.J. Zhang, Z.Y. Zhou, Microscopic
[69,70]. Moreover, Eib of BCZT-7 ceramics is obviously lower than insight into electric fatigue resistance and thermally stable piezoelectric
that of BCZT-3 and BCZT-5 ceramics. Finally, compared to BCZT-3 properties of (K,Na)NbO3-based ceramics, ACS Appl. Mater. Interfaces 10
and BCZT-5 ceramics, the hysteresis loop area of BCZT-7 ceramics (2018) 28772e28779.
[11] I. Coondoo, S. Satapathy, N. Panwar, Impact of tin substitution on the struc-
decreases significantly after 106 cycles, which implies that BCZT-7 tural, dielectric, ferroelectric and piezoelectric properties of Ba0.98Ca0.02TiO3
ceramics require less energy to reverse polarization [58]. ceramics, Physica B 553 (2019) 68e75.
[12] L. Jin, J. Qiao, L. Hou, L. Wang, L. Zhang, X. Lu, H.L. Du, X.Y. Wei, Y. Yan, G. Liu,
High electrostrictive effect in La3þ-doped Ba(Zr0.2Ti0.8)O3 lead-free ferroelec-
4. Conclusions trics, J. Alloys Compd. 776 (2019) 599e605.
[13] W.F. Liu, X.B. Ren, Large piezoelectric effect in Pb-free ceramics, Phys. Rev.
BCZT ceramics with super large and uniform grains have been Lett. 103 (2009) 257602.
[14] K. Castkova, K. Maca, J. Cihlar, H. Hughes, A. Matousek, P. Tofel, Y. Bai,
synthesized by sol-gel method. The effects of pH value of precursor T.W. Button, Chemical synthesis, sintering and piezoelectric properties of
solution on microstructure, electric properties and bipolar fatigue Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free ceramics, J. Am. Ceram. Soc. 98 (2015)
behavior were systematically studied. BCZT powders with the 2373e2380.
[15] S.B. Li, C.B. Wang, L. Li, Q. Shen, L.M. Zhang, Effect of annealing temperature on
particle size of 136e221 nm were prepared by controlling the pH
structural and electrical properties of BCZT ceramics prepared by plasma
value and the particle size decreases with the increase of pH value. activated sintering, J. Alloys Compd. 730 (2018) 182e190.
BCZT ceramics prepared by BCZT powders with large particle size [16] I. Coondoo, N. Panwar, D. Alikin, I. Bdikin, S.S. islam, A. Turygin, V.Y. Shur,
have super large grain size (35e55 mm), and the grain size and A.L. Kholkin, A comparative study of structural and electrical properties in
lead-free BCZT ceramics: influence of the synthesis method, Acta Mater. 155
densification of BCZT ceramics decrease as the pH value increases. (2018) 331e342.
The construction of phase boundary of BCZT ceramics is obviously [17] Y.C. Liu, Y.F. Chang, F. Li, B. Yang, Y. Sun, J. Wu, S.T. Zhang, R.X. Wang,
affected by pH value. The diffuseness behavior of BCZT ceramics W.W. Cao, Exceptionally high piezoelectric coefficient and low strain hys-
teresis in grain-oriented (Ba,Ca)(Ti,Zr)O3 through integrating crystallographic
enhances with the increase of pH value. The remnant polarization texture and domain engineering, ACS Appl. Mater. Interfaces 9 (2017)
and coercive electric field of BCZT ceramics decrease with the in- 29863e29871.
crease of pH value, which is mainly caused by effects of grain size. [18] W.F. Bai, D.Q. Chen, P. Li, B. Shen, J.W. Zhai, Z.G. Ji, Enhanced electrome-
chanical properties in <00l>-textured (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free
BCZT ceramics prepared by precursor solution with a pH of 5 have piezoceramics, Ceram. Int. 42 (2016) 3429e3436.
outstanding piezoelectric properties (d33 ¼ 585.6 pC/N and [19] A. Hamza, F. Benabdallah, I. Kallel, L. Seveyrat, L. Lebrun, H. Khemakhem,
d*33 ¼ 898 pm/V), which can be correlated to the coexistence of T Effect of rare-earth substitution on the electrical properties and Raman
spectroscopy of BCTZ ceramics, J. Alloys Compd. 735 (2018) 2523e2531.
and O phase and its super large grain size (50 mm). Moreover, BCZT [20] M.X. Zhou, R.H. Liang, Z.Y. Zhou, C.H. Xu, X. Nie, X.L. Dong, Enhanced Curie
ceramics with large grain size has high fatigue resistance to bipolar temperature and piezoelectric properties of (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-
electric cycling. free ceramics after the addition of LiTaO3, Mater. Res. Bull. 106 (2018)
213e219.
[21] W.F. Bai, L.J. Wang, P. Zheng, F. Wen, L.L. Li, J.W. Zhai, Z.G. Ji, Electromechanical
Acknowledgements response and piezoelectric properties in (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezocer-
amics using nano-sized AlN modification, Ceram. Int. 44 (2018)
16040e16050.
This work was supported by Excellent Talent Project in Uni-
[22] Y. Zhang, H.J. Sun, W. Chen, A brief review of Ba(Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3
versity of Chongqing (Grant No. 2017-35), the Science and Tech- based lead-free piezoelectric ceramics: past, present and future perspectives,
nology Innovation Project of Social Undertakings and People’s J. Phys. Chem. Solids 114 (2018) 207e219.
Livelihood Guarantee of Chongqing (Grant No. [23] Z. Liu, R.H. Yuan, D.Z. Xue, W.W. Cao, T. Lookman, Origin of large electrostrain
in Sn4þ doped Ba(Zr0.2Ti0.8)O3-x(Ba0. 7Ca0.3)TiO3 ceramics, Acta Mater. 157
cstc2017shmsA90015), the Program for Innovation Teams in Uni- (2018) 155e164.
versity of Chongqing (Grant No. CXTDX201601032), the Leading [24] X. Ji, C.B. Wang, S.B. Li, S. Zhang, R. Tu, Q. Shen, J. Shi, L.M. Zhang, Structural
552 Q. Zhang et al. / Journal of Alloys and Compounds 794 (2019) 542e552

and electrical properties of BCZT ceramics synthesized by solegel process, (2015) 64e67.
J. Mater. Sci. Mater. Electron. 29 (2018) 7592e7599. [47] X.Z. Fu, W. Cai, G. Cheng, R.L. Gao, Effects of Sn doping on the microstructure
[25] E. Chandrakala, J.P. Praveen, B.K. Hazra, D. Das, Effect of sintering temperature and dielectric and ferroelectric properties of Ba(Zr0.2Ti0.8)O3 ceramics,
on structural, dielectric, piezoelectric and ferroelectric properties of solegel J. Mater. Sci. Mater. Electron. 28 (2017) 8177e8185.
derived BZT-BCT ceramics, Ceram. Int. 42 (2016) 4964e4977. [48] H. Orihara, S. Hashimoto, Y. Ishibashi, A theory of D-E hysteresis loop based on
[26] S. Hunpratub, S. Phokha, S. Maensiri, P. Chindaprasirt, Dielectric and piezo- the Avrami model, J. Phys. Soc. Jpn. 63 (1994) 1031e1035.
electric properties of lead-free Ba0.85Ca0.15Ti0.9xZr0.1CuxO3 ceramics syn- [49] J.W. Zhai, X. Yao, J. Shen, L.Y. Zhang, H. Chen, Structural and dielectric prop-
thesized by a hydrothermal method, Appl. Surf. Sci. 369 (2016) 334e340. erties of Ba (ZrxTi1x)O3 thin films prepared by the solegel process, J. Phys. D
[27] P. Jaimeewong, P. Boonsong, P. Ngernchuklin, R. Tipakontitikul, Enhanced Appl. Phys. 37 (2004) 748e752.
sinterability and electrical properties of Bi2O3-added Ba0.85Ca0.15Zr0.1Ti0.9O3 [50] G.H. Haertling, Ferroelectric ceramics: history and technology, J. Am. Ceram.
ceramics, Ferroelectrics 511 (2017) 88e93. Soc. 82 (1999) 797e818.
[28] P. Jaimeewong, M. Promsawat, A. Watcharapasorn, S. Jiansirsomboon, [51] Y. Zhang, M. Xie, J. Roscow, C. Bowen, Dielectric and piezoelectric properties of
Comparative study of properties of BCZT ceramics prepared from conven- porous lead-free 0.5Ba(Ca0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 ceramics, Mater. Res.
tional and sol-gel auto combustion powders, Integr. Ferroelectr. 175 (2016) Bull. 112 (2019) 426e431.
25e32. [52] E.W. Yap, J.L. Glaum, J. Oddershede, J.E. Daniels, Effect of porosity on the
[29] P. Bharathi, K.B.R. Varma, Grain and the concomitant ferroelectric domain size ferroelectric and piezoelectric properties of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 piezo-
dependent physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics fabricated electric ceramics, Scripta Mater. 145 (2018) 122e125.
using powders derived from oxalate precursor route, J. Appl. Phys. 116 (2014) [53] L. Jin, W.T. Luo, L. Wang, Y. Tian, Q.Y. Hu, L. Hou, L. Zhang, X. Lu, H.L. Du,
164107. X.Y. Wei, G. Liu, Y. Yan, High thermal stability of electric field-induced strain
[30] Z.M. Wang, J.J. Wang, X.L. Chao, L.L. Wei, B. Yang, D.W. Wang, Z.P. Yang, in (1x)(Bi0.5Na0.5)TiO3-xBa0.85Ca0.15Ti0.9Zr0.1O3 lead-free ferroelectrics, J. Eur.
Synthesis, structure, dielectric, piezoelectric, and energy storage performance Ceram. Soc. 39 (2019) 277e286.
of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramics prepared by different methods, J. Mater. [54] J.H. Gao, Q. Li, H.R. Liu, J. Shim, Q.F. Yan, Y.L. Zhang, X.C. Chu, Enhanced
Sci. Mater. Electron. 27 (2016) 5047e5058. temperature stability in Tb-doped (Ba0.99Ca0.01)(Ti0.98Zr0.02)O3 lead free ce-
[31] J.P. Praveen, K. Kumar, A.R. James, T. Karthik, S. Asthana, D. Das, Large ramics, Ceram. Int. 41 (2015) 2497e2501.
piezoelectric strain observed in solegel derived BZTeBCT ceramics, Curr. [55] C.L. Zhao, H. Wang, J.G. Xiong, Composition-driven phase boundary and
Appl. Phys. 14 (2014) 396e402. electrical properties in (Ba0.94Ca0.06)(Ti1exMx)O3 (M¼ Sn, Hf, Zr) lead-free
[32] J.G. Hao, W.F. Bai, W. Li, J.W. Zhai, Correlation between the microstructure and ceramics, Dalton Trans. 45 (2016) 6466e6480.
electrical properties in high-performance (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 lead-free € del, X.R. Xing, Critical
[56] H. Liu, J. Chen, L.L. Fan, Y. Ren, Z. Pan, K.V. Lalitha, J. Ro
piezoelectric ceramics, J. Am. Ceram. Soc. 95 (2012) 1998e2006. role of monoclinic polarization rotation in high-performance perovskite
[33] H.L. Sun, Q.J. Zheng, Y. Wan, X. Wu, K.W. Kwok, H.L. Chan, D.M. Lin, Corre- piezoelectric materials, Phys. Rev. Lett. 119 (2017), 017601.
lation of grain size, phase transition and piezoelectric properties in [57] P. Li, J.W. Zhai, B. Shen, S.J. Zhang, X.L. Li, F.Y. Zhu, X.M. Zhang, Ultrahigh
Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics, J. Mater. Sci. Mater. Electron. 26 (2015) piezoelectric properties in textured (K,Na)NbO3-based lead-free ceramics,
5270e5278. Adv. Mater. 30 (2018) 1705171.
[34] V. Bijalwan, P. Tofel, J. Erhart, K. Maca, The complex evaluation of functional [58] N. Chaiyo, D.P. Cann, N. Vittayakorn, Lead-free (Ba,Ca)(Ti,Zr)O3 ceramics
properties of nearly dense BCZT ceramics and their dependence on the grain within the polymorphic phase region exhibiting large, fatigue-free piezo-
size, Ceram. Int. 45 (2019) 317e326. electric strains, Mater. Des. 133 (2017) 109e121.
[35] X.D. Yan, M.P. Zheng, S.Q. Sun, M.K. Zhu, Y.D. Hou, Boosting energy harvesting € del, X.L. Tan, An ideal amplitude window against electric
[59] Z. Fan, J. Koruza, J. Ro
performance in (Ba,Ca)(Ti,Zr)O3 lead-free perovskite through artificial control fatigue in BaTiO3-based lead-free piezoelectric materials, Acta Mater. 151
of intermediate grain size, Dalton Trans. 47 (2018) 9257e9266. (2018) 253e259.
[36] P. Jaimeewong, M. Promsawat, S. Jiansirisomboon, A. Watcharapasornad, In- €del,
[60] V. Rojas, J. Koruza, E.A. Patterson, M. Acosta, X.J. Jiang, N. Liu, C. Dietz, J. Ro
fluence of pH values on the surface and properties of BCZT nanopowders Influence of composition on the unipolar electric fatigue of Ba(Zr0.2Ti0.8)O3-
synthesized via sol-gel auto-combustion method, Surf. Coating. Technol. 306 (Ba0.7Ca0.3)TiO3 lead-free piezoceramics, J. Am. Ceram. Soc. 100 (2017)
(2016) 16e20. 4699e4709.
[37] C.L. Liu, X. Liu, D. Wang, Z.H. Chen, B.J. Fan, J.L. Ding, X.Y. Zhao, H.Q. Xu, [61] Y.C. Zhang, J. Glaum, M.C. Ehmke, J.E. Blendell, K.J. Bowman, M.J. Hoffman,
H.S. Luo, Improving piezoelectric property of BaTiO3eCaTiO3eBaZrO3 lead- High bipolar fatigue resistance of BCTZ lead-free piezoelectric ceramics, J. Am.
free ceramics by doping, Ceram. Int. 40 (2014) 9881e9887. Ceram. Soc. 99 (2016) 174e182.
[38] W.F. Bai, D.Q. Chen, J.J. Zhang, J.S. Zhong, M.Y. Ding, B. Shen, J.W. Zhai, Z.G. Ji, [62] J.Q. Zhao, Z.X. Yue, W.Q. Wang, Z.L. Gui, L.T. Li, Characterizations of fatigue and
Phase transition behavior and enhanced electromechanical properties in crack growth of ferroelectrics under cyclic electric field, J. Electroceram. 21
(Ba0.85Ca0.15)(ZrxTi1-x)O3 lead-free piezoceramics, Ceram. Int. 42 (2016) (2008) 581e584.
3598e3608. [63] H. Simons, J. Glaum, J.E. Daniels, A.J. Studer, A. Liess, J. Ro € del, M. Hoffman,
[39] X.D. Yan, M.P. Zheng, Y.D. Hou, M.K. Zhu, Composition-driven phase boundary Domain fragmentation during cyclic fatigue in 94%(Bi1/2Na1/2)TiO3-6%BaTiO3,
and its energy harvesting performance of BCZT leadefree piezoelectric J. Appl. Phys. 112 (2012), 044101.
ceramic, J. Eur. Ceram. Soc. 37 (2017) 2583e2589. [64] Z.H. Luo, J. Glaum, T. Granzow, W. Jo, R. Dittmer, M. Hoffman, J. Ro €del, Bipolar
[40] Y.W. Liu, Y.P. Pu, Z.X. Sun, Enhanced relaxor ferroelectric behavior of BCZT and unipolar fatigue of ferroelectric BNT-based lead-free piezoceramics, J. Am.
lead-free ceramics prepared by hydrothermal method, Mater. Lett. 137 (2014) Ceram. Soc. 94 (2011) 529e535.
128e131. [65] S. Pojprapai, J. Glaum, The effect of temperature on bipolar electrical fatigue
[41] M.H. Frey, D.A. Payne, Grain-size effect on structure and phase trans- behavior of lead zirconate titanate ceramics, Funct. Mater. Lett. 5 (2012)
formations for barium titanate, Phys. Rev. B 54 (1996) 3158e3167. 1250027.
[42] H.T. Martirenat, J.C. Burfoot, Grain-size effects on properties of some ferro- [66] N. Balke, H. Kungl, T. Granzow, D.C. Lupascu, M.J. Hoffmann, J. Ro €del, Bipolar
electric ceramics, J. Phys. C Solid State Phys. 7 (1974) 3182e3192. fatigue caused by field screening in Pb(Zr,Ti)O3 ceramics, J. Am. Ceram. Soc. 90
[43] W.R. Buessem, L.E. Cross, A.K. Goswami, Phenomenological theory of high (2007) 3869e3874.
permittivity in fine-grained barium titanate, J. Am. Ceram. Soc. 75 (1992) [67] Z. Luo, T. Granzow, J. Glaum, W. Jo, J. Ro €del, M. Hoffman, Effect of ferroelectric
2923e2926. long-range order on the unipolar and bipolar electric fatigue in Bi1/2Na1/2TiO3-
[44] P. Sharma, P. Kumar, R.S. Kundu, J.K. Juneja, N. Ahlawat, R. Punia, Structural based lead-free piezoceramics, J. Am. Ceram. Soc. 94 (2011) 3927e3933.
and dielectric properties of substituted barium titanate ceramics for capacitor [68] Q.Y. Jiang, E.C. Subbarao, L.E. Cross, Grain size dependence of electric fatigue
applications, Ceram. Int. 41 (2015) 13425e13432. behavior of hot pressed PLZT ferroelectric ceramics, Acta Mater. 42 (1994)
[45] Y.T. Lin, X.R. Miao, N. Qin, H. Zhou, W.L. Deng, D.H. Bao, Effects of Mn doping 3687e3694.
on structural and dielectric properties of solegel-derived [69] L. Chen, H.Q. Fan, Q. Li, Characterization of acceptor-doped (Ba,Ca)TiO3 “hard”
(Ba0.835Ca0.165)(Zr0.09Ti0.91)O3 thin films, Thin Solid Films 520 (2012) piezoelectric ceramics for high-power applications, Ceram. Int. 43 (2017)
5146e5150. 5579e5584.
[46] H. Kaddoussi, Y. Gagou, A. Lahmar, J. Belhadi, B. Allouche, J.L. Dellis, M. Courty, [70] Z.H. Zhao, Y.J. Dai, F. Huang, The formation and effect of defect dipoles in lead-
H. Khemakhem, M.E. Marssi, Room temperature electro-caloric effect in lead- free piezoelectric ceramics: a review, Sustain. Mater. Tech. 20 (2019), e00092.
free Ba(Zr0.1Ti0.9)1xSnxO3 (x¼0, x¼0.075) ceramics, Solid State Commun. 201