Phase coexistence and large piezoelectricity in BaTiO 3 -CaSnO 3 lead-free ceramics

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1 Received: 14 September 2017 Accepted: 26 December 2017 DOI: /jace ORIGINAL ARTICLE Phase coexistence and large piezoelectricity in BaTiO 3 -CaSnO 3 lead-free ceramics Yang Yang 1 Yibei Zhou 1 Juan Ren 1 Qiaoji Zheng 1 Kwok Ho Lam 2 Dunmin Lin 1 1 College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, China 2 Department of Electrical Engineering, The Hong Kong Polytechnic University, Hunghom, Kowloon, Hong Kong Correspondence Dunmin Lin, College of Chemistry and Materials Science, Sichuan Normal University, Chengdu, China. ddmd222@sicnu.edu.cn and Kwok Ho Lam, Department of Electrical Engineering, The Hong Kong Polytechnic University, Hunghom, Kowloon, Hong Kong. kokokh.lam@polyu.edu.hk Funding information National Natural Science Foundation of China, Grant/Award Number: ; Science & Technology Department of Sichuan Province, Grant/Award Number: 2016JY0225; Education Department of Sichuan Province, Grant/Award Number: 15ZA0034, 15ZA0037; The Hong Kong Polytechnic University, Grant/Award Number: 1-ZVGH Abstract Ferroelectric phase coexistence was constructed in (1 x)batio 3 -xcasno 3 leadfree ceramics, and its relationship with the piezoelectricity of the materials was investigated to ascertain potential factors for strong piezoelectric response. It is found that the addition of CaSnO 3 caused a series of phase transitions in the (1 x)batio 3 -xcasno 3 ceramics, and a ferroelectric coexistence of rhombohedral, orthorhombic, and tetragonal phases is formed at x = 0.08, where the ceramics exhibit the lowest energy barrier and consequently facilitate the polarization rotation and extension, resulting in the optimal piezoelectricity of d 33 and k p values of 550 pc/n and 0.60, respectively. Our study provides an intuitive insight to understand the origin of high piezoelectricity in the ceramics with the coexistence of multiferroelectric phases. KEYWORDS barium titanate, lead-free ceramics, perovskites, phase transition, piezoelectric materials/properties 1 INTRODUCTION Lead zirconate titanate (PZT)-based perovskite ceramics possess excellent permittivity and piezoelectricity near the morphotropic phase boundary (MPB), 1 and thus have been widely used in ceramic filters, transducers, actuators, transformers, and sensors. 2,3 However, the high content of toxic lead in the PZT-based ceramics have raised environmental and health concerns. 4-7 Thus, it is necessary to develop lead-free ceramics with good piezoelectricity. Among leadfree perovskite materials, BaTiO 3 -based ceramics have attracted considerable attention due to their tunable phase structures and excellent piezoelectricity. Especially, in 2009, Ren et al 8 found that Ba(Zr 0.2 Ti 0.8 )O 3 -(Ba 0.7 Ca 0.3 ) TiO 3 (BZCT) lead-free ceramics possess ultrahigh piezoelectric properties (d 33 ~ 620 pc/n) near the morphotropic phase boundary (MPB). This means that it is very promising to develop perovskite lead-free ceramics with high piezoelectric properties to replace Pb-based piezoelectric ceramics. In BZCT ceramics, early crystallographic studies suggest a coexisting of R and T for the high-property MPB composition So it can be known that the construction of phase boundary is one of the effective methods to promote the piezoelectric properties of lead-free ceramics. 12 However, it is confused for the mechanism for ultrahigh piezoelectric properties of the BZCT ceramics near the The American Ceramic Society wileyonlinelibrary.com/journal/jace J Am Ceram Soc. 2018;101:

2 YANG ET AL MPB. In 2011, Ren et al 9 continue to study the BZCT ceramics, and they found that the high piezoelectric properties can be attributed to the low polarization anisotropy as well as the elastic softening at MPB. Recently, an intermediate orthorhombic phase has been discovered within a narrow composition/temperature regime in the BCZT system by high-resolution XRD or anelastic measurement. 13,14 On the other hand, the MPB has been also reported as a T-R boundary in Ba(Ti,Sn)O 3 -x(ba,ca)tio 3 systems. 15,16 But the orthorhombic phase is also expected according to the characteristics of phase transition for BaTiO 3 -based ceramics. In recent years, increasing attention has been paid to BaTiO 3 (BT)-based lead-free piezoelectric ceramics. One of the main reasons is that pure BaTiO 3 ceramics undergoes four phase transitions with the temperature increases from 90 to 130 C, in which the detailed transformations are as follows: rhombohedral (R) phase transforms into orthorhombic (O) phase at 90 C, O phase transforms into tetragonal (T) phase at 5 C, and T phase transforms into cubic (C) phase at 130 C. 17 Many investigations have been carried out to construct the phase boundary in the BTbased ceramics using different categories of additives, resulting in the enhancement of piezoelectricity For example, when the BT material are codoped with Ca 2+ and Zr 4+ or Ca 2+ and Sn 4+, the materials such as (Ba,Ca)(Ti, Zr)O 8,9 3 and (Ba,Ca)(Ti,Sn)O show a high piezoelectric coefficient d 33 of larger than 400 pc/n. In general, the substitutions of Ca 2+ for Ba 2+ and Zr 4+ and/or Sn 4+ for Ti 4+ lead to the simultaneous shift of R-O and O-T phase transitions toward high temperatures at different rates and thus the R-T biphase boundary is formed; as a result, the enhanced piezoelectricity is exhibited near the R-T phase boundary 21,22 Based on the polarization deflection theory proposed by Fu and Cohen, the increasing number of spontaneous polarization direction would induce stronger piezoelectricity for perovskite piezoelectric ceramics. 24 According to the phase transition nature of BT, it is highly possible to form a coexistence of three ferroelectric phases (tetragonal, orthorhombic, and rhombohedral phases) in BT-based ceramics by optimizing the shift rate of R-O and O-T phase transitions toward room temperature. This is conducive to understanding the origin of the enhanced piezoelectric properties near the phase boundary. In this work, CaSnO 3 was introduced into BT to increase the temperatures of R-O and O-T phase transitions to form a series of coexistences of two or three phases at room temperature; and the phase structure and its relationship with the piezoelectricity of the materials was investigated. Our study shows that a ferroelectric coexistence of tetragonal, orthorhombic, and rhombohedral was constructed in the (A) (B) (C) FIGURE 1 SEM images of the BTCS-x ceramics with x = (A) 0, (B) 0.08, and (C) 0.14

3 2596 YANG ET AL. (1 x)batio 3 -xcasno 3 material with x = 0.08, where high d 33 and k p values of 550 pc/n and 0.60, respectively, can be attained because of the lowest energy barrier within the three ferroelectric phases coexistence. 2 EXPERIMENTAL PROCEDURE (1 x)batio 3 -xcasno 3 (abbreviated as BTCS-x) lead-free ceramics were prepared by a conventional solid-state reaction using BaCO 3 (99.86%), CaCO 3 (99.85%), TiO 2 (99.88%), and SnO 2 (99.50%) as raw materials. The raw material powders in stoichiometric proportion of BTCS-x were mixed, and then ball-milled in ethanol for 8 hours. After dried, the mixture was calcined at 1100 C for 4 hours, and then ball-milled again in ethanol for 10 hours. The calcined mixture was then mixed with polyvinyl alcohol (PVA) binder solution, and pressed into disks with the diameter of 10 mm diameter and the thickness of 1 mm. After the removal of the binder, the samples were sintered at 1350 C for 2 hours, and then coated with silver electrodes. Before piezoelectric measurements, the samples were poled under a dc field of 3 kv/mm at room temperature for 30 minutes in a silicone oil bath. The phase structure of the sintered ceramics was analyzed by an X-ray diffractometer (XRD) with CuKa (k = A) radiation (Smart Lab; Rigaku, Japan). The temperature dependence of relative permittivity e r was evaluated at 1 khz using an LCR meter (Agilent E4980A; Agilent Technologies Inc, Malaysia) with a temperature controlled probe stage (LinkamTS1500E; Linkam Scientific Instruments Ltd, UK) from 120 to 150 C. The microstructure of the ceramics was measured using scanning electron microscopy (FEI-Quanta250; FEI, the Netherlands). The planar electromechanical coupling factor k p was measured by the resonance method according to the IEEE Standards 176 using an impedance analyzer (Agilent 4294A; Agilent Inc). Ferroelectric hysteresis loops were measured by a precision ferroelectric workstation (Premier II; Radiant Technologies Inc, USA). The piezoelectric charge constant d 33 was measured with a quasistatic piezoelectric meter (ZJ-6A; Chinese Academic Society, China) for the poled samples. The differential scanning calorimetry (DSC) curves of the ceramics were measured by a differential scanning calorimeter (Discovery DSC, America). The Raman spectra of the ceramics were recorded using a Renishaw 2000 (UK) spectrometer at the room temperature. 3 RESULTS AND DISCUSSION The SEM images of the ceramics with x = 0, 0.08 and 0.14 are shown in Figure 1. It can be clearly observed that the microstructure of BTCS-x ceramics is mightily dependent on the amount of CaSnO 3. All ceramics can be well-sintered at 1350 C for 2 hours and exhibit a relatively dense structure. The average grain size of pure BT ceramics (x = 0) is >100 lm. With x increasing, the average grain sizes of the BTCS-x ceramics become small, indicating that the addition of CaSnO 3 could inhibit the grain growth. Figure 2 shows the XRD patterns of the BTCS-x ceramics at environmental temperature (room temperature FIGURE 2 A, XRD patterns of the BTCS-x ceramics with 0 x 0.14 and B, the enlarged view of selected diffraction peaks at 2h = [Color figure can be viewed at wileyonlinelibrary.com]

4 YANG ET AL FIGURE 3 XRD fitting patterns of BTCS-x ceramics in the 2h range of with A, x =0;B,x = 0.02; C, x = 0.04; D, x = 0.06; E, x = 0.08; F, x = 0.10; G, x = 0.12; H, x = 0.14[Color figure can be viewed at wileyonlinelibrary.com] about 12 C). A pure perovskite structure is detected for all BTCS-x ceramics. As x increases, the diffraction peaks shift toward higher angle, which is correlated with the lattice shrinkage because of much smaller radii of Ca 2+ (0.99 A) 25 compared with that of Ba 2+ (1.35 A). 26 According to the results of XRD, it can be preliminarily ascertained that the BTCS-x ceramics exhibit the coexistence of the orthorhombic (O) and tetragonal (T) phases at 0.00 x The existence of O phase in pure ceramic may be caused by the phase transition of tetragonal and orthorhombic phases at ~5 C. In general, pure BaTiO 3 material exhibits a perovskite structure with tetragonal symmetry. However, from Figure 5A, there is a phase transition of tetragonal and orthorhombic phases at ~5 C. At the time of measurement, the environmental temperature in our city is about 12 C, which is close to the phase transition temperature of tetragonal and orthorhombic phases. Therefore, it is possible that the pure BaTiO 3 ceramic possesses a perovskite structure with tetragonal and orthorhombic symmetries in this study. At x = 0.08, the ceramic possesses a ferroelectric three phases coexistence of tetragonal, orthorhombic and rhombohedral (R-O-T) phases. When x increases to 0.10, the phase structure of the ceramics is transformed into the coexistence of orthorhombic (O) and rhombohedral (R) phases. And rhombohedral and cubic (C) phase boundary exists at 0.12 x To clarify the phase structure, the XRD peaks of BTCS-x ceramics in the ranges of were fitted by Peakfit software using the least-squares approach. As shown in Figure 3, the peaks between 44.5 and 46 can be fitted into (002) T /(200) T, (022) O /(200) O, (202) R and (200) C peaks. With x increasing from 0 to 0.10, the integrated intensity of (002) T /(200) T peaks increases continuously, while the intensity of (022) O /(200) O peaks decreases markedly. In addition, with x increasing, these peaks exhibit an offset, leading to the partial overlap of the peaks, such as (200) O and K a2 peaks at 0.06 x 0.10 and (200) T and (202) R peaks at x = It can be seen that the (202) R peaks appear at x 0.08, whereas the (200) C peaks appear at x 0.12, suggesting that rhombohedral and cubic phases exist at x 0.08 and 0.12, respectively.

5 2598 YANG ET AL. FIGURE 4 (A), (C) and (E) Rietveld refinement for the (1-x)BaTiO 3 -xcasno 3 ceramics with x = 0, 0.08, and 0.10 in the 2h of 20-70, respectively; (B), (D) and (F) the enlarged view of selected diffraction peaks in the 2h = for the ceramics with x = 0, 0.08, and 0.10, respectively [Color figure can be viewed at wileyonlinelibrary.com] TABLE 1 Refined structural parameters of the (1 x)batio 3 -xcasno 3 ceramics at x = 0, 0.08, and 0.10 x SG a ( A) b ( A) c ( A) a (= b = c) Content Volume ( A 3 ) v 2 R p (%) R wp (%) 0 P4mm % Amm % P4mm % Amm % R3m Amm % R3m % Based on the XRD patterns as shown in Figure 2, the full-pattern matching was conducted by the General Structure Analysis System (GSAS) software package. Figure 4 shows the Rietveld refinement results for the BaTiO 3 -x ceramics with x = 0, 0.08, and 0.10, whereas the crystal structure parameters derived from the Rietveld refinements

6 YANG ET AL are shown in Table 1. For the material with x = 0, the goodness-of-fit indicators of v 2, R wp (%), and R p (%) are calculated to be 2.26, 5.92, and 4.51, respectively, suggesting a good matching between the observed and calculated patterns. Furthermore, it can be found from Figure 4A,B that the pure BT ceramics (x = 0) shows the coexistence of the orthorhombic (O) and tetragonal (T) phases, but the O phase content is relatively small, only 22.71%. From Figure 4C,D, it is clearly observed that R (R3m), O (Amm2), and T (P4 mm) phases coexist in the 0.92BaTiO CaSnO 3 ceramic. The phase contents of R, O and T phases are 25.23%, 46.27%, and 28.50%, respectively. These results indicate that the R-O-T ferroelectric phase coexistence is formed at x = In addition, as x further increases to 0.10, the ceramics have been transformed from three ferroelectric phase (R-O-T) coexistence to two ferroelectric phase (R-O) coexistence (Figure 4E,F), and the O phase and R phase contents are 64.63% and 34.37%, respectively. FIGURE 5 e r -T curves of the BTCS-x ceramics (the insets are the corresponding enlarged peak(s) of e r -T curves) with A, x =0;B,x = 0.02; C, x = 0.04; D, x = 0.06; E, x = 0.08; F, x = 0.10; G, x = 0.12; H, x = 0.14 [Color figure can be viewed at wileyonlinelibrary.com]

7 2600 YANG ET AL. To further verify the phase transition behavior induced by the addition CaSnO 3, the temperature dependence of relative permittivity e r was measured and the results are shown in Figure 5. One can see that there are three obvious dielectric peaks, corresponding to the rhombohedral-orthorhombic (R- O) phase transition at T R-O, the orthorhombic-tetragonal (O- T) phase transition at T O-T, and the tetragonal-cubic phase transition at T C, respectively. From Figure 5A, it is easily found that the orthorhombic-tetragonal (O-T) phase transition is situated at ~5 C. Because the measure temperature of XRD is about 12 C (the temperature in our city is ~12 C in winter), the O-T phase transition does not completely disappear, resulting in the O-T phase coexistence of the pure BaTiO 3 ceramic. As x increases, both the R-O and O-T peaks shift toward high temperature at different rates, whereas the T C peak moves to low temperature with x increasing. Eventually, when x = 0.12, the T R-O and T O-T peaks merge into a single peak (T R-O-T ). In general, for BT-based ceramics, the grain size would have the direct effect on the Curie temperature of the materials, that is, smaller grain size leads to lower Curie temperature. In addition, the partial substitution of Sn 4+ for Ti 4+ leads to the central symmetry of some unit cells at room temperature. 30 These may be responsible for the shift of ferroelectric-paraelectric phase transition toward low temperature with x increasing. The phase transitions of the ceramics were also confirmed by measuring the DSC curves of the ceramics at 80 to 180 C and the results are shown in Figure 6A. It can easily be seen from Figure 6A that there are three endothermic peaks, corresponding to the R-O, O-T, and T- C phase transitions, respectively. With x increasing, the peak intensities reduce gradually, and all peaks shifted toward room temperature and ultimately merge into one peak. The variations in phase transformation energy of R-O and O-T with x for the BTCS-x ceramics are exhibited in Figure 6B. One can notice that whether R-O or O-T, the variations in phase transformation energy have similar trend in which the energy firstly decreases and then increases. The R-O and O-T curves are getting closer with x increasing, and even overlap when x = In addition to the overlapping of R-O and O-T curves, the phase transformation energies of R-O or O-T phase transitions reach the identical minimum value of J/g when x = Figure 6C shows the phase diagram of the BTCS-x based on the temperature-dependent dielectric properties (e r -T) and the DSC curves of the ceramics. It can be found that the results obtained from the relative permittivity and DSC curves are very similar, which make good agreement from each other. As x increases, both T R-O and T O-T increase, whereas the T C shows a monotonically decreasing trend. When x = 0.08, T R-O and T O-T merge together (T R-O-T ) near room temperature, indicating that the R-O-T ferroelectric three phases coexist at room temperature. FIGURE 6 A, DSC curves and B, variations in phase transformation energy of R-O and O-T of the BTSC-x ceramics; C, the phase diagram of the BTSC-x ceramics originated from the results of the permittivity and the DSC with x [Color figure can be viewed at wileyonlinelibrary.com] Figure 7A displays the Raman spectra of the BTCS-x ceramics, while the enlarged spectra at the wave number of cm 1 and the variation in the vibration modes

8 YANG ET AL FIGURE 7 A, Room-temperature Raman spectra of BTCS-x ceramics with x; B, the enlarged drawing at wavelength of cm 1 ; C, the variation in the vibration modes with x [Color figure can be viewed at wileyonlinelibrary.com] with x are shown in Figure 7B,C, respectively. As wellknown, the pure BT possesses a perovskite structure at room temperature, and each unit cell contains five atoms. 31 Therefore, for the pure BT, there are 12 kinds of optical vibration mode (3F 1u + 1F 2u ). 31 When the phase structure of the materials transforms to T phase, the F 1u splits into the A 1 and E modes, and F 2u splits into the B 1 and E modes. 32 In addition, all A 1 and E modes exhibit Raman and infrared activities, and B 1 mode only shows the Raman activity. 33 However, the A 1 and E modes further split into horizontal (TO) and vertical (LO) optical modes due to the existence of the short coherence length and long-range electrostatic force. 34 When the T phase structure transforms into the O phase structure, the optical model belongs to the symmetrical A 1, A 2, B 1, B 2, which are Raman active. When the phase structure is the R phase, there are A 1 and E modes derived from F 1u modes, which are also Raman active. 35 From Figure 7A, six Raman peaks can be observed, orderly corresponding to the following vibration modes: E (TO 1 ), A 1 (TO 1 ), A 1 (TO 2 ), E (TO 2 ), A 1 (TO 3 ), and A 1 (LO 3 )/E (LO 3 ). The characteristic peaks of the tetragonal BT ceramics corresponds to the situation: ~120 cm 1, ~170 cm 1, ~268 cm 1, ~305 cm 1, ~517 cm 1, and ~719 cm 1, 18 as shown in Figure 7C. As x increases to 0.06, the A 1 (TO 1 ) and A 1 (TO 2 ) peaks disappear, indicating that the phase structure transforms from the T phase into the O phase. When x = 0.08, the E (TO 2 ) peak exhibits a blue shift, illustrating that the R phase exists. However, the characteristic peak of T phase (A 1 (LO 3 )/E (LO 3 )) still exists at x = 0.08, suggesting the coexistence of the R-O-T phase. With x further increasing to 0.10, the A 1 (LO 3 )/E (LO 3 ) peak is weak, indicating that the T phase is absent, and thus the O and R phase coexist. Furthermore, at 0.12 x 0.14, the E (TO 2 ) peak disappears while other peaks are weakened, suggesting the appearance of the C phase and the absence of the O phase. These results are in agreement with the XRD, temperaturedependent e r and DSC results of the ceramics. The polarization-electric field (P-E) hysteresis loops of the BTCS-x ceramics are displayed in Figure 8A-H. With x increasing, the P-E loops become more and more slender. At x = 0.14, the loop almost becomes a curve, illustrating that the phase of the ceramics has been transformed into the paraelectric phase. The variations in remanent polarization (P r ) and coercive electric field (E c )withx are exhibited in Figure 8I. As x increases, the P r firstly increases and reaches a maximum value of 19.0 lc/cm 2 at x = 0.02, and then decreases gradually. E c keeps decreasing as x increases, and even approaches zero at x = Figure 9A displays the variations in d 33 and k p of the BTCS-x ceramics. Both the d 33 and k p exhibit the same trend that firstly increases and then declines as x increases from 0 to When x = 0.08, the d 33 and k p exhibits the maximum values of 550 pc/n and 0.60, respectively. The 0.92BaTiO CaSnO 3 ceramic possesses the optimal piezoelectric properties with the coexistence of three ferroelectric phases (R-O-T). Based on the polarization deflection theory proposed by Fu and Cohen, 24 the more spontaneous polarization directions would give the lower polarization rotation energy barrier. When the ferroelectric phases coexist in the perovskite piezoelectric materials, the low polarization rotation energy barrier would lead to the easy transformation between ferroelectric phases. For the ceramic with x = 0.08, three ferroelectric phases, including

9 2602 YANG ET AL. R, O and T phases, coexist in which the R phase has eight spontaneous polarization directions in the <111>, the O phase has twelve spontaneous polarization directions in the <110>, and the T phase has six spontaneous polarization directions in the <001>. Hence, the coexistence region of three ferroelectric phases has 24 polarization directions, which is much larger than that of the ferroelectric biphase boundary. Therefore, when the ceramic is poled under the external electric field, the movement and inversion of the ferroelectric domain would become much easier, resulting in an enhancement of piezoelectric performance and thus obtaining outstanding piezoelectric properties. 36 On the other hand, based on the thermodynamics theory, the coexistence of three ferroelectric phases has the lowest free energy, ie, the lowest energy barrier. 37 From the DSC results as shown in Figure 5B, one can easily observe that the energy barrier of three ferroelectric phase coexistence is much lower than that of two ferroelectric phase coexistence, indicating that the thermodynamic energy state is a flattening behavior near the three phase coexistence. This leads to the easy rotation of ferroelectric domains within the R-O-T coexistence, and thus enhances the piezoelectric properties of the material. Figure 9B shows the variations in relative permittivity e r and loss tangent tand of the BTCS-x ceramics. The e r is shown to increase significantly from 1613 to with x increasing from 0 to There are two reasons for large dielectric response at x = 0.14: (i) the content of C phase is larger than other components. The permittivity value at T C is largest, which can also be found its implication from Figure 5. Based on the Landau-Ginzburg thermodynamic model calculations, 38,39 for the ferroelectric phase composition, the energy barrier completely disappears near T C, and the vanishing of energy barrier can facilitate a large FIGURE 8 A-H, Ferroelectric hysteresis loops of BTCS-x ceramics with x; I, variations in P r and E c of BTCS-x ceramics with x [Color figure can be viewed at wileyonlinelibrary.com]

10 YANG ET AL Therefore, the variation in the d 33 of 0.92BaTiO CaSnO 3 ceramic with annealing temperature (T a ) was studied, and the result is shown in Figure 10. The d 33 value was measured at room temperature after annealing for 1 hour at every evaluated temperature. It is observed that the d 33 firstly increases, reaching a maximum value of 580 pc/n, when T a increases from room temperature to 40 C, and then with further increasing the T a, the d 33 exhibits a downtrend. As temperature is gradually close to Curie temperature, ferroelectric domains are switched back to the initial state. 44 This leads to the degradation of the piezoelectricity of the ceramic. 4 CONCLUSIONS FIGURE 9 A, Variations in d 33 and k p, and B, variations in e r and tand of BTCS-x ceramics with x [Color figure can be viewed at wileyonlinelibrary.com] (1 x)batio 3 -xcasno 3 lead-free ceramics with large piezoelectricity have been prepared by a conventional solid-state method. The ceramics exhibit the coexistence of T-O phases at 0 x As x further increases to 0.08, the coexistence of tetragonal, orthorhombic and rhombohedral ferroelectric phases is developed. The coexistence of three ferroelectric phases greatly enhances the piezoelectric properties of the materials. The optimal piezoelectric performance (d 33 = 550 pc/n and k p = 0.60) of (1 x)batio 3 -xcasno 3 ceramics is acquired at x = 0.08, which is attributed to more spontaneous polarization directions and the lowest energy barrier induced by the three phases coexistence of R, O, andt phases. ACKNOWLEDGMENTS FIGURE 10 Variations in d 33 with annealing temperature (T a ) ( C) of the poled 0.92BaTiO CaSnO 3 ceramic [Color figure can be viewed at wileyonlinelibrary.com] polarization change in the presence of the electric field resulting in larger permittivity. (ii) this is attributed to the formation of adaptive states under the condition of the near-vanishing polarization anisotropy near the ferroelectric-paraelectric phase coexistence region, which is the reason for large intrinsic and extrinsic dielectric property In addition, the tand decreases with x increasing, reaching the minimum value of ~1.37% at x = Large piezoelectric response for the 0.92BaTiO CaSnO 3 ceramic with d 33 of 550 pc/n has been observed due to the coexistence of R, O, and T three ferroelectric phases, which may has potential application. 8,43 This work was supported by the projects of National Natural Science Foundation of China (Grant No ), Science & Technology Department of Sichuan Province (2016JY0225), Education Department of Sichuan Province (15ZA0034, 15ZA0037), and The Hong Kong Polytechnic University (1-ZVGH). ORCID Dunmin Lin REFERENCES 1. Eitel RE, Randall CA, Shrout TR, et al. New high temperature morphotropic phase boundary piezoelectrics based on Bi(Me)O 3 PbTiO 3 ceramics. Jpn J Appl Phys. 2001;40: Lin D, Kwok KW, Chan HLW. Structure, dielectric and piezoelectric properties of Ba 0.90 Ca 0.10 Ti 1 x Sn x O 3 lead-free ceramics. Ceram Int. 2014;40: Lin D, Zheng Q, Li Y, et al. Microstructure, ferroelectric and piezoelectric properties of Bi 0.5 K 0.5 TiO 3 -modified BiFeO 3

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