An Alternative Way To Enhance Piezoelectricity and Temperature

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

An Alternative Way To Enhance Piezoelectricity and Temperature Stability in Lead-Free Sodium Niobate Piezoceramics Xiang Lv,† Yanbin Chen,† Bo Wu,‡ Jianguo Zhu,† Dingquan Xiao,† and Jiagang Wu*,† †

Department of Materials Science, Sichuan University, Chengdu 610065, P. R. China Sichuan Province Key Laboratory of Information Materials and Devices Application, Chengdu University of Information Technology, Chengdu 610225, P. R. China

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‡

ABSTRACT: To further balance the relationship between piezoelectricity and temperature stability, the (0.975 − y)NaNbO3-yBaTiO3-0.025BaZrO3 (y = 0−0.20) ceramics are developed by constructing a wide tetragonal phase region. Effects of BaTiO3 on the relationships among phase structure, electrical properties, and temperature dependence are investigated. With increasing BaTiO3 contents, the ceramics endure the structural evolutions from orthorhombic phase to tetragonal phase, and then to relaxor cubic phase. A wide tetragonal phase zone of 24−180 °C can be realized in the ceramics with y = 0.08, together with an enhanced piezoelectric coefficient d33 = 215 pC/N. Intriguingly, excellent temperature stability of unipolar strain (Suni) and piezoelectric coefficient (d33) are observed in the ceramics with y = 0.08 within 20−180 °C. This work provides an alternative way to enhance piezoelectricity and temperature stability in lead-free piezoceramics.

1. INTRODUCTION The requirement of environmental protection restricts the content of lead in electronic devices owing to its high toxicity.1 Lead-free piezoceramics {including potassium sodium-niobate (KNN), barium titanate (BT), and sodium bismuth titanate (BNT)} are developed to replace the part lead-containing ones.2 For example, superior d33 values (e.g., 400−700 pC/N) are found in KNN- and BT-based piezoceramics, which mainly originate from the construction of multiphase coexistence.3−5 Giant strain (e.g., 0.70%) can be achieved in BNT-2.5Nb ceramics, which originates from the involvement of phase transition from ergodic relaxor to ferroelectric phase under an electric field.6 Unfortunately, a strong temperature dependence of piezoelectric effect is often followed in the above-mentioned ceramics.3,5−7 Generally, two methods are used to achieve both enhanced piezoelectricity and good temperature stability in piezoceramics. The first one is to construct a morphotropic phase boundary (MPB) that is widely reported in lead-based ceramics, and the second one is to fabricate the highly textured ceramics or single crystal.8−10 It is difficult or disadvantageous for lead-free piezoelectric ceramics to achieve any one of two ways, due to the temperature-dependent phase transition as well as high cost and complicated process of the second method.11−13 Therefore, an alternative way to simultaneously boost the piezoelectricity and temperature stability at a low cost is highly desired.13−15 Let us return back to the evolution of lead-free piezoceramics. For pure K0.5Na0.5NbO3 ceramics, d33 values (≤103 pC/N) can remain almost unchanged within both orthorhombic (O) and © XXXX American Chemical Society

tetragonal (T) phase zones due to their own temperature ranges and relatively stable dielectric permittivity (εr) (Figure 1a).16 The similar phenomenon is also reported in (0.9 − x)NaNbO3-0.1BaTiO3-xCaZrO3 ceramics.17 Low variation (≤16.5%) of d33 (≤158 pC/N) can be found in 0.9NN0.1BT ceramic within 25−220 °C due to its wide T phase zone (Figure 1b). Although a morphotropic phase boundary consisting of rhombohedral and tetragonal (e.g., R and T) phases elevates the d33 value of NaNbO3-based ceramics to 231 pC/N, a relatively low Tc of 144 °C is observed, shortening the temperature range for applications (Figure 1c).17 Therefore, if one can construct a single phase at a wider temperature range without significantly reducing its piezoelectricity, a satisfying overall-performance may be highly anticipated. Recently, it is reported that the addition of appropriate BaZrO3 could increase the contents of the ferroelectric phase in NaNbO3 ceramics.18 Therefore, an improved piezoelectricity and a single phase with a wide temperature range are highly expected if we further add ferroelectric BaTiO3 into NN-BZ ceramics and carefully control its content. In this work, we fabricate the (0.975 − y)NaNbO3-yBaTiO3-0.025BaZrO3 (y = 0−0.20) ceramics by the conventional solid reaction method, and a wide T phase region can be established by controlling BaTiO3 contents. Effects of BaTiO3 contents on the relationships among phase structure, electrical properties, and temperature dependence are importantly investigated. Through subtly tailoring the BaTiO3 contents, an improved d33 Received: June 8, 2018

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DOI: 10.1021/acs.inorgchem.8b01602 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 1. Temperature-dependent εr and d33 of (a) K0.5Na0.5NbO3, (b) 0.9NaNbO3-0.1BaTiO3, and (c) CaZrO3-doped NaNbO3-BaTiO3 ceramics.

(e.g., 215 pC/N) and favorable temperature stability {e.g., an almost unchanged unipolar strain (Suni) within 20−180 °C} can be realized, and the related physical mechanisms are also discussed.

2. EXPERIMENTAL PROCEDURE The detailed fabrication process of (0.975 − y)NaNbO3-yBaTiO30.025BaZrO3 [NN-yBT-BZ, y = 0−0.20] ceramics can be easily found in our previous publications.3,4,7 The characterizations for composition-dependent XRD patterns (at room temperature), temperaturedependent εr (εr−T) curves, piezoelectricity {e.g., d33 and planar electromechanical coupling factor (kp)}, ferroelectric hysteresis (P− E) loops, and strain curves are also described in detail in our previous work.3,4,7 To measure the XRD patterns of the 0.895NaNbO30.08BaTiO3-0.025BaZrO3 ceramic at different temperatures, the assintered disks are grinded into powder. Then, the fine powder is annealed at 600 °C for 1 h to remove the strain introduced by grinding. Subsequently, the powder XRD data are measured using an X’ Pert PRO MPD (PANalytical, Netherlands), which is equipped with an external temperature controller. Finally, in situ temperaturedependent variations of d33 values are collected using a self-built apparatus, which was introduced in previous literature.19 The commercial PIC151 ceramics are bought from PI Piezo Technology company (Lederhose, Germany).

3. RESULTS AND DISCUSSION Figure 2a exhibits the composition-dependent XRD patterns of (0.975 − y)NN-yBT-0.025BZ ceramics. A typical perovskite structure is observed in all samples without other obvious secondary phases. To clearly observe the evolutions of phase structure, the XRD patterns with different 2θ ranges are enlarged, as shown in Figure 2b−d. It is found that XRD patterns gradually shift toward a lower angle, mainly due to the overwhelming radii difference between barium (Ba2+) and sodium (Na+) ions (CN = 12, rBa = 0.161 nm, rNa = 0.139 nm; CN = 6, rZr = 0.072 nm, rTi = 0.0605 nm) (Figure 2c,d).18,20 Evidently, the composition with y = 0 displays an O phase, which is proved to be the coexistence of antiferroelectric orthorhombic P and ferroelectric orthorhombic Q phases.18 The increase of BT contents gradually decreases the intensity of the O phase’s diffraction peaks (Figure 2b) and changes the phase structure into a tetragonal-like phase at y = 0.07 (Figure 2b,d).18,21 Then, the splitting peaks converge into a single one at y ≥ 0.15, manifesting the emergence of pseudo-cubic (or cubic) phase (Figure 2c,d).22 ε r −T curves are used to further demonstrate the identification of phase structures (Figure 3a−i). Without the addition of BT, two dielectric anomalies (labeled as T1 and T2) are found (Figure 3a), which, respectively, represent ferro-

Figure 2. (a) Composition-dependent XRD data of NN-yBT-BZ ceramics, and magnified views with (b) 2θ = 35−41°, (c) 2θ = 51.5− 52.5°, and (d) 2θ = 45.5−46.5°.

electric (Q)-antiferroelectric (P) phase transition temperature and Curie temperature (Tc).18 After the addition of BT, three dielectric anomalies {e.g., rhombohedral-orthorhombic (TR‑O) and orthorhombic-tetragonal (TO‑T) transition temperatures, as well as Tc} are clearly found in the composition with y = 0.05.17,21 Furthermore, TR‑O and TO‑T are far away from room temperature, further proving the existence of an O phase at ambient temperature. With an increase of BT contents, TR‑O, TO‑T, and Tc gradually reduce. TO‑T values of 58 and 42 °C close to room temperature are, respectively, observed in the compositions with y = 0.07 and 0.075 (Figure 3d), indicating the existence of orthorhombic phase. Considering the tetragonal-like diffraction peaks in the compositions with y = B


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Inorganic Chemistry

Figure 3. (a−i) Variations of permittivity (εr) with increasing temperature from −150 to 200 °C of NN-yBT-BZ ceramics, measured at 0.1−100 kHz.

increases up to 200 °C, both splitting {200}PC and {220}PC diffraction peaks change into a single one (Figure 4b,c), indicating ferroelectric-paraelectric phase transition.24 Considering the increasing relaxor behavior, the relaxor behavior is evaluated by a modified Curie law

0.07 and 0.075 (Figure 1d), these two compositions reasonably possess an orthorhombic-tetragonal (O-T) phase coexistence.23 As y increases up to 0.125, TR‑O and TO‑T converge into a single dielectric anomaly with obvious relaxor behavior (Figure 3g), indicating a T phase at room temperature. Finally, only one dielectric anomaly (Tc) is observed at y = 0.15−0.20. A Tc of 50 °C (Figure 3h) and single diffraction peak within 2θ = 44−46° (Figure 1d) suggest a coexistence phase that is composed of tetragonal phase and relaxor cubic phase in the composition with y = 0.15, which is subsequently supported by the saturated P−E loop (Figure 6a) and obvious d33 (Figure 7a). However, the composition with y = 0.20 exhibits a relaxor cubic phase due to its Tc of −1 °C (Figure 3i) and vanished piezoelectricity (Figure 7a). To further testify the increasing T phase zone (y = 0.08− 0.125), in situ powder XRD patterns of the composition with y = 0.08 are measured with varied temperatures (25−200 °C) (Figure 4a). {200}PC and {220}PC peaks are magnified to clearly show the evolution of phase structure (Figure 4b,c). An intensity ratio of 1:2 between (002)T and (200)T remains unchanged at 25−180 °C, suggesting a stable T phase structure within 25−180 °C (Figure 4b).24 The similar tendency is also observed in {220}PC diffraction peaks with an opposite intensity ratio (Figure 4c). As the temperature

(T − Tm)γ 1 1 − = ε(T ) εm C

where εm is the maximum εr, Tm is the temperature value at εm, and C is a constant.25 Degree of diffuseness (γ) is within 1−2. The higher γ is, the more diffuseness there is. γ of a classical ferroelectric is 1, while γ of 2 represents an ideal relaxor.25 Figure 5a displays the linear fittings between log(T − Tm) and log(1/ε − 1/εm). The inset of Figure 5a displays the variations of γ. It is found that γ gradually increases with increasing BT contents. A γ of ∼2 is observed at y = 0.20, suggesting an ideal relaxor.25 The phase diagram of NN-yBT-BZ ceramics (y ≥ 0.05) is depicted according to the variations of TR‑O, TO‑T, and Tc (Figure 5b). With increasing BT contents, both O and R phase zones reduce, while T and C phase zones expand. The room-temperature phase structure can be defined as follows: an O phase at y = 0−0.06, an O-T coexistence phase at y = 0.07−0.075, a T phase at y = 0.08−0.125, a T-C coexistence phase at y = 0.15, and a relaxor C phase at y = 0.20. Figure 6a shows P−E loops of NN-yBT-BZ ceramics varying with y. Without BT (y = 0), a poor P−E loop is observed owing to the antiferroelectric O phase (P).18,26 With increasing BT contents, P−E loops gradually become saturated. Particularly, the saturated P−E loop is found at y = 0.125. However, the further increase of BT contents makes P−E loops slender, which is caused by the increasing content of relaxor C phase. The evolutions of remanent polarization and coercive field (e.g., Pr and Ec) of NN-yBT-BZ ceramics are depicted in Figure 6b. It is found that Ec gradually reduces with increasing BT contents. However, Pr first increases and then reduces, resulting in the maximum value of 11.8 μC/cm2 at y = 0.125. The observed high Ec at the O phase zone is due to the necessary high field (approximately 60−100 kV/cm) that can

Figure 4. (a) Powder XRD patterns of the composition with y = 0.08 at increasing temperature (25−200 °C). Enlarged views with (b) 2θ = 45−47° and (c) 2θ = 66.5−68°. C


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Inorganic Chemistry

Figure 5. (a) Linear fittings between log(T − Tm) and log(1/ε − 1/εm) in NN-yBT-BZ ceramics. The inset displays the variation of diffuseness degree (γ). (b) Phase diagram of NN-yBT-BZ ceramics with y ≥ 0.05.

Figure 7. (a) d33 and (b) εr and tan δ of NN-yBT-BZ ceramics varying with y. (c) In situ temperature-dependent d33 and εr of 0.895NaNbO3-0.08BaTiO3-0.025BaZrO3 ceramics. (d) Normalized in situ d33 of 0.895NaNbO3-0.08BaTiO3-0.025BaZrO3 ceramics and other representative piezoelectric ceramics.

Figure 6. (a) P−E loops and (b) Pr and Ec of NN-yBT-BZ ceramics.

induce the antiferroelectric-ferroelectric phase transition.26 As the phase structure changes from O phase into T phase, no antiferroelectric-ferroelectric phase transition can be observed, resulting in lower Ec in the T phase zone. On the other hand, the degree of relaxor (γ) increases with increasing BT content, which probably could further promote domain switching and reduce Ec.25,27 Similarly, the variation of Pr is also mainly due to the evolution of phase structure. Relatively low electric field (E = 40 kV/cm) cannot induce the antiferroelectric-ferroelectric phase transition, resulting in a nonsaturated P−E loop in the ceramics y = 0 (Figure 6b). Such a nonsaturated P−E loop at low electric field is mainly caused by the dielectric loss.28 The addition of BT gradually increases the contents of the ferroelectric phase and changes O phase into T phase, accounting for the increasing Pr values at y = 0.05−0.125. It is worth noting that an obvious Pr of 9.7 μC/cm2 is observed at y = 0.15, accompanying with a relatively saturated P−E loop (Figure 6a,b). This phenomenon is probably attributed to its Tc of 50 °C that is slightly higher than room temperature, indicating an easy relaxor-ferroelectric phase transition under an external electric field, which is further proved by an observable d33 value of 85 pC/N (Figure 7a).29 Further reduction of Tc (−6 °C) at y = 0.20 generates in an ideal relaxor C phase, accounting for the negligible Pr and Ec (Figure 6b). Figure 7a shows the d33 values of NN-yBT-BZ ceramics varying with y. Without BT (y = 0), a d33 of 0 pC/N is

observed due to the lack of antiferroelectric-ferroelectric phase transition that needs a higher electric field (e.g., E = 60−100 kV/cm).26 The observable d33 values are induced after the addition of BT (Figure 7a). Upon the increasing BT content, d33 first increases at y = 0−0.08 and then reduces at y = 0.08− 0.20, resulting in the maximum value of 215 pC/N at y = 0.08. Figure 7b displays the dielectric permittivity (εr) and loss factor (tan δ) of NN-yBT-BZ ceramics. εr gradually increases at y = 0−0.15 and then reduces at y > 0.15. The observed maximum εr at y = 0.15 is mainly due to its Tc (50 °C) approaching room temperature (Figure 3h). In addition, tan δ of NN-yBT-BZ ceramics remains at the values less than 0.04 (Figure 7d). In situ temperature-dependent small signal d33 is important for the piezoelectric sensor application.2,13 Previously, the publications usually examine the ex situ temperature-dependent d33 values to evaluate the thermal stability by annealing at different temperatures.21,30 In this work, a self-built instrument is employed to collect in situ variations of d33 values of the poled samples (y = 0.08) (Figure 7c).19 Two samples of the ceramics with y = 0.08 exhibit the coincident variation; that is, d33 first reduces slightly, then sharply increases at T − Tc, and finally drops to zero at T ≥ Tc. The εr−T curve is added to explain the origin of in situ temperature-dependent d33 (Figure 7c). εr first remains stable at T = 25−125 °C, then sharply increases at T ∼ Tc, and finally decreases at T ≥ Tc. Thus, the D


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Inorganic Chemistry

transition (as proved by the saturated P−E loop and observable d33 = 85 pC/N).18,29 In addition, H gradually reduces with increasing BT contents, resulting in low H of ≤10% at y = 0.08−0.20. Such an H value is lower than other lead-free ceramics (e.g., H values of 10−18% in KNNTL ceramics), indicating the potential applications for precise control.34 Figure 8c,e, respectively, displays the unipolar strain curves of the compositions with y = 0.08 and 0.15, measured at different temperatures. The corresponding variations of Suni and S(T)/S(RT) are shown in Figure 8d,f. One can see that a stable Suni is observed in the samples with y = 0.08 at T = 20− 180 °C (Figure 8c,d), suggesting a favorable temperature stability. However, Suni of the ceramics with y = 0.15 first increases at T ≤ Tc and then reduces at T > Tc, resulting in an unstable Suni at T = 20−180 °C. Here, the stable Suni at y = 0.08 mainly attributes to the wide T phase zone within 20−180 °C and benign stabilization of εr. However, the strong temperature dependence of strain behavior in the ceramics with y = 0.15 originates from low Tc of 50 °C. As a result, constructing a single phase within a wide temperature range is an effective way to reinforce the temperature stability of piezoelectricity. Figure 9a−d shows the unipolar strain curves of the composition with y = 0.08, measured at different electric fields and temperatures. At a given electric field, the maximum Suni values of unipolar strain curves almost remain unchanged, which is highly similar to that of Sm-doped PMN-31PT ceramics with an MPB.8 Figure 9e lists the detailed variations of normalized temperature-dependent Suni of the ceramics as a function of electric fields. It is found that the normalized Suni slightly fluctuates around 100% for all electric fields, further suggesting the ideal temperature stability. Finally, we compare the temperature stability of NN-0.08BT-BZ ceramics with other outstanding lead-free (and lead-containing) ceramics, as show in Figure 9f.3,9,31,35−37 Suni of PZT-4 ceramics gradually increases with increasing temperatures,9 whereas our ceramics (e.g., NN-0.08BT-BZ) display an almost unchanged Suni. Although the improved piezoelectricity and temperature stability can be found in KNN-based ceramics with rhombohedral-tetragonal phase coexistence, the temperaturedependent phase transition will inevitably result in a gradually reduced S uni with increasing temperatures (Figure 9f).3,9,31,35−37 In this work, a wide T phase zone and benign stabilization of εr are achieved in the composition with y = 0.08, resulting in an almost unchanged Suni at T = 20−180 °C, which is superior to lead-free KNN-based ceramics. Considering such a favorable temperature stability of d33 and Suni, NN0.08BT-BZ ceramics are promising for the applications of sensors and actuators.

stable d33 at y = 0.08 below its Tc mainly originates from its wide T phase zone and stable εr (Figure 7c). Figure 7d exhibits the temperature stability of d33 of representative lead-free and lead-based (e.g., PIC151) ceramics. One can see that a stable d33 is observed in PIC151 ceramics below its Tc, due to the involvement of a typical MPB.19 It is worth noting that both KNN- and BT-based ceramics display the obvious temperature sensibility owing to the character of temperature-dependent phase boundary.31−33 Here, a stable variation of d33 is obtained in poled samples with y = 0.08, which mainly stems from the wide T phase region and stable εr. Such a temperature insensitivity is superior to those of other lead-free piezoceramics. Hence, the good temperature independence of piezoelectricity can be achieved by constructing a relatively wide tetragonal phase region. Figure 8a exhibits the unipolar strain curves of NN-yBT-BZ ceramics with different y. Figure 8b depicts the variations of

Figure 8. (a) Unipolar strain curves and (b) Suni and H of NN-yBTBZ ceramics. Temperature-dependent unipolar strain curves of NNyBT-BZ ceramics with (c) y = 0.08 and (e) y = 0.15. Corresponding variations of Suni and normalized Suni of NN-yBT-BZ ceramics with (d) y = 0.08 and (f) y = 0.15.

4. CONCLUSION (0.975 − y)NaNbO3-yBaTiO3-0.025BaZrO3 (y = 0−0.20) ceramics are prepared by the conventional solid sintering method, and effects of BaTiO3 contents on the relationships among phase structure, electrical properties, and temperature dependence are studied. The increase of BaTiO3 contents changes the phase structure of ceramics from an O phase to a T phase, and then to a relaxor C phase. The 0.895NaNbO30.08BaTiO3-0.025BaZrO3 ceramics exhibit a wide T phase zone within 24−180 °C and an increased d33 of 215 pC/N. Such a wide T phase zone is demonstrated by temperaturedependent XRD patterns and εr−T curves. In addition, an almost unchanged Suni and a slightly reduced d33 are

unipolar strain (Suni) and relative hysteresis (H). H is determined by the following equation H=

ΔSE/2 Smax

× 100%

where Smax is the maximum Suni and ΔSE/2 is the difference of Suni at half of Emax (e.g., maximum electric field).34 With increasing BT contents, Suni appears two peaks in the compositions with y = 0.08 and y = 0.125, respectively. The first peak is mainly attributed to the improved piezoelectricity (e.g., d33 = 215 pC/N), while the second one probably stems from the electric-field-induced paraelectric-ferroelectric phase E


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Inorganic Chemistry

Figure 9. (a−d) Temperature-dependent unipolar strain curves and (e) normalized Suni of 0.895NaNbO3-0.08BaTiO3-0.025BaZrO3 ceramics under different electric fields. (f) Temperature stability of Suni of this work and other representative piezoceramics including lead-containing and lead-free. (5) Li, P.; Zhai, J.; Shen, B.; Zhang, S.; Li, X.; Zhu, F.; Zhang, X. Ultrahigh Piezoelectric Properties in Textured (K,Na)NbO3-Based Lead-Free Ceramics. Adv. Mater. 2018, 30, 1705171. (6) Liu, X.; Tan, X. Giant Strains in Non-Textured (Bi1/2Na1/2)TiO3-Based Lead-Free Ceramics. Adv. Mater. 2016, 28, 574−578. (7) Zheng, T.; Wu, W.; Wu, J.; Zhu, J.; Xiao, D. Balanced development of piezoelectricity, Curie temperature, and temperature stability in potassium−sodium niobhrate lead-free ceramics. J. Mater. Chem. C 2016, 4, 9779−9787. (8) Li, F.; Lin, D.; Chen, Z.; Cheng, Z.; Wang, J.; Li, C.; Xu, Z.; Huang, Q.; Liao, X.; Chen, L. Q.; et al. Ultrahigh piezoelectricity in ferroelectric ceramics by design. Nat. Mater. 2018, 17, 349. (9) Saito, Y.; Takao, H.; Tani, T.; Nonoyama, T.; Takatori, K.; Homma, T.; Nagaya, T.; Nakamura, M. Lead-free piezoceramics. Nature 2004, 432, 84−87. (10) Liu, H.; Veber, P.; Rödel, J.; Rytz, D.; Fabritchnyi, P. B.; Afanasov, M. I.; Patterson, E. A.; Frömling, T.; Maglione, M.; Koruza, J. High-performance piezoelectric (K,Na,Li)(Nb,Ta,Sb)O3 single crystals by oxygen annealing. Acta Mater. 2018, 148, 499−507. (11) Zheng, T.; Wu, J. Enhanced piezoelectricity over a wide sintering temperature (400−1050 °C) range in potassium sodium niobate-based ceramics by two step sintering. J. Mater. Chem. A 2015, 3, 6772−6780. (12) Yuan, Y.; Wu, J.; Hong, T.; Lv, X.; Wang, X.; Lou, X. Composition design and electrical properties in (1-y)(K0.40Na0.60)0.985Li0.015(Nb1−xSbx)O3-yBi0.5Na0.5ZrO3 lead-free ceramics. J. Appl. Phys. 2015, 117, 084103. (13) Koruza, J.; Bell, A. J.; Frömling, T.; Webber, K. G.; Wang, K.; Rödel, J. Requirements for the transfer of lead-free piezoceramics into application. J. Materiomics. 2018, 4, 13−26. (14) Li, J. F.; Wang, K.; Zhu, F. Y.; Cheng, L. Q.; Yao, F. Z. (K,Na)NbO3-Based Lead-Free Piezoceramics: Fundamental Aspects, Processing Technologies, and Remaining Challenges. J. Am. Ceram. Soc. 2013, 96, 3677−3696. (15) Acosta, M.; Novak, N.; Rojas, V.; Patel, S.; Vaish, R.; Koruza, J.; Rossetti, G., Jr.; Rödel, J. BaTiO3-based piezoelectrics: Fundamentals, current status, and perspectives. Appl. Phys. Rev. 2017, 4, 041305. (16) Yin, J.; Wu, J.; Wang, H. Composition dependence of electrical properties in (1-x)KNbO3-xNaNbO3 lead-free ceramics. J. Mater. Sci.: Mater. Electron. 2017, 28, 4828−4838. (17) Zuo, R.; Qi, H.; Fu, J. Morphotropic NaNbO3-BaTiO3-CaZrO3 lead-free ceramics with temperature-insensitive piezoelectric properties. Appl. Phys. Lett. 2016, 109, 022902. (18) Dou, M.; Fu, J.; Zuo, R. Electric field induced phase transition and accompanying giant poling strain in lead-free NaNbO3-BaZrO3 ceramics. J. Eur. Ceram. Soc. 2018, 38, 3104−3110.

simultaneously observed in 0.895NaNbO3-0.08BaTiO3-0.025BaZrO3 ceramics within the temperature range of 20−180 °C, which is due to a wide T phase region and relatively stable εr. Therefore, this work can introduce an alternative and low-cost way to enhance piezoelectricity and weaken temperature sensibility in lead-free piezoceramics.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. ORCID

Jiagang Wu: 0000-0002-9960-9275 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is accomplished with the support of the National Natural Science Foundation of China (NSFC Nos. 51722208 and 51332003), the Key Technologies Research and Development Program of Sichuan Province (No. 2018JY0007), and the Graduate Student’s Research and Innovation Fund of Sichuan University (Nos. 2012017yjsy111 and 2018YJSY009). The authors appreciate the support from Prof. Jürgen Rödel’s group (Technische Universität Darmstadt, Germany) for providing the apparatus that can measure in situ unipolar strain curves and small signal d33 at different temperatures.

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REFERENCES

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