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Phase structure regulation and enhanced piezoelectric properties of Li-doped KNN-based ceramics
Materials Chemistry and Physics 245 (2020) 122806
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Phase structure regulation and enhanced piezoelectric properties of Li-doped KNN-based ceramics Rujie Zhao a, b, Yuanliang Li a, b, *, Zhanshen Zheng a, b, Wenshuo Kang a, b a
Key Lab of Environment Functional Materials of Tangshan City, 063210, Hebei, China Hebei Provincial Key Lab of Inorganic Nonmetallic Materials, College of Materials Science and Engineering, North China University of Science and Technology, Tangshan, 063210, Hebei, China
b
H I G H L I G H T S
� 0.96(K0.48Na0.52-xLix)NbO3-0.04Bi0.5Na0.5ZrO3(KNLxN-BNZ) ceramics was successfully synthesized. � The phase transition temperature TO-T and TC of the ceramics were shifted by Liþ doped. � KNL0.03N-BNZ ceramic has a lower TO-T and a higher coexistence proportion of O-T phase. � The highest proportion of two phases coexistence is the most efficient. � KNL0.03N-BNZ ceramic has a high TC while achieving high piezoelectric performance. A R T I C L E I N F O
A B S T R A C T
Keywords: Ceramics Phase transitions Raman spectroscopy Electrical properties
0.96(K0.48Na0.52-xLix)NbO3-0.04Bi0.5Na0.5ZrO3 (KNLxN-BNZ) lead-free ceramics have been synthesized by traditional solid-state reaction. Here, the relationship between phase composition and piezoelectric performance of ceramics is explored systematically. Analysis of XRD and Raman spectroscopy confirmed that the orthogonal (O) phase and the tetragonal (T) phase coexisted in each sample at room temperature. By studying the function curve of temperature and dielectric constant εr, it is found that the introduction of Liþ in ceramics can have a lower O-T phase transition temperature (TO-T) and a higher Curie temperature (TC), with the TO-T closest to room temperature and the highest coexistence volume proportion of O-T phase in the ceramic when x ¼ 0.03, which had the optimum values for d33 ¼ 252 pC/N and TC ¼ 382 � C. Due to the excellent piezoelectric properties and high TC, it is believed that KNLxN-BNZ piezoceramics can have great application prospects at high temperatures.
1. Introduction Piezoelectric ceramics are outstanding functional ceramics, mainly in the fields of transducers, actuators and sensors [1–4]. Lead-free piezoelectric ceramics are the ultimate development goal due to the sustainable development of human beings [5–8]. The KNN-based ((K, Na)NbO3) piezoelectric ceramics have become one of the research hot spot systems to replace PZT materials by its high TC, excellent piezo electric properties and ferroelectric properties [1,6–13]. However, compared with PZT ceramics, the comprehensive performance of KNN-based ceramics still needs further improvement. For KNN-based ceramics, the greatest concern is the establishment of a polycrystalline phase boundary at room temperature, just like the morphotropic phase boundary in PZT ceramics [8,14,15]. Due to the polycrystalline phases
coexisting, the spontaneous polarization directions in the ceramic in crease, the domain rotates easily under the external electric field, then the piezoelectric performance is enhanced [16,17]. Previous articles have reported that the pure KNN ceramic undergoes three phase tran sitions with temperature changes, and all phase transition temperatures of pure KNN ceramics are kept away from room temperature [7]. Studies have shown that the TO-T can be shifted by doping the second component in KNN ceramics, thus establishing an O-T phase boundary at room temperature. Liþ is one of them [18–20]. Especially, KNN ceramics modified by Li(NaK)NbO3 [21] or LiSbO3–KNN [22] exhibit a large d33 and high kp value due to the O-T phase boundary being established. In addition, compounds such as (Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 [23], CaZrO3 [24] and (Bi0.5Na0.5)ZrO3 [25] can be doped to control the phase composition of KNN ceramics and construct the
* Corresponding author. Key Lab of Environment Functional Materials of Tangshan City, 063210, Hebei, China. E-mail addresses: [email protected] (R. Zhao), [email protected] (Y. Li), [email protected] (Z. Zheng), [email protected] (W. Kang). https://doi.org/10.1016/j.matchemphys.2020.122806 Received 20 December 2019; Received in revised form 4 February 2020; Accepted 12 February 2020 Available online 13 February 2020 0254-0584/© 2020 Elsevier B.V. All rights reserved.
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Materials Chemistry and Physics 245 (2020) 122806
rhombohedral-tetragonal(R-T) phase boundary, further optimizing the piezoelectric properties. When the components are located at the O-T or R-T phase boundary, the polarization direction of the ceramics can be more easily deflected between different symmetries, thus improving the piezoelectric properties. However, it is worth noting that some modified KNN ceramics mentioned above will be accompanied by a lower TC, which is not conducive to high-temperature applications. Therefore, it is necessary to realize large piezoelectricity and higher TC in KNN-based ceramics after modification. In this paper, a binary material system of KNLxN-BNZ piezoceramics with high TC was synthesized using the traditional sintering method. The evolution of crystal structure, grain size, multiphase coexistence behavior and piezoelectric performance of samples after doping of Liþ were studied. The structure of the O-T phase boundary was proved by XRD and Raman spectroscopy. In addition, the grain size and the phase transition temperature (TO-T and TC) of the KNLN-BNZ ceramics changed significantly with the doping of Liþ. Whereafter, the relationship be tween the coexistence proportion the of O-T phase and electrical per formance in ceramics was explored, and the internal mechanism was analyzed in depth.
Fig. 1. (a) XRD patterns of the KNLxN-BNZ ceramics; (b) Enlarged XRD pat terns in the range of 2θ from 44.5� to 46.5� .
that a phase transition has occurred in these ceramics, and all the ceramic samples were considered to possess an O-T phase boundary. The intensity ratio of the two peaks at x ¼ 0.03 is almost 1:1, indicating that the proportion of O-T phase coexisting in ceramics under this compo nent is the highest. There is an abnormal trend in the intensity variation of the two peaks at x ¼ 0.05, which may be due to the formation of K3Li2Nb5O15 affecting the transition of phase structure. To further confirm the results of the XRD analysis, Raman spectros copy in the range of 100–1000 cm 1 was performed on all ceramic samples, as shown in Fig. 2(a). All the vibration modes of NbO6, such as 1A1g(ν1)þ1Eg(ν2)þ2F1u(ν3,ν4)þF2g(ν5)þF2u(ν6) [28] were observed, where theν1 mode represents a symmetric stretching vibration of NbO6, which can determine the phase transition evolution [29] and ν5 repre sents a bending vibration mode of NbO6 [30], presented in Fig. 2(b). Fig. 2(c) demonstrates the variation of Raman shift with x of the A1g(ν1) and F2g(ν5) modes. It is observed that as the x increases to 0.03, the ν1 peak gradually shifts to a higher wave number and then decreases when x ¼ 0.05. The variation in Raman shift reflects the change in the distance between atoms in the oxygen octahedron or the variation in the chem ical bond angle between atoms. The reduction in Raman shift is accompanied by an increase in the spacing between atoms and vice versa. Fig. 2(d) shows the function of the refined cell parameter “c” and the crystal axis ratio c/a with the x content. The decrease of “c” indicates that the oxygen octahedron compressed along the direction of <001>, and the distance between the two oxygen atoms is reduced. The result was also consistent with the evolution of the ν1 peak in Fig. 2(c). The reason is that Liþ with smaller radius replaces the A-site of the KNN-BNZ ceramic, which leads to the fact that the crystal lattice of the KNN-BNZ ceramic as a whole exhibits the oxygen octahedron compression to the center and transforms into the T-phase. Anomalous changes in the Raman shift of the ν5 modes and the crystal axis ratio c/a further illus trate that the O-T phase exists in all samples. Fig. 3(a) demonstrates the εr-T curves of the KNLxN-BNZ ceramics, measured at 1 kHz. It can be observed that each of the εr-T curves has two obvious dielectric peaks corresponding to the TO-T and TC. For all ceramics, the TO-T (58 � C-107 � C) is close to room temperature, which proved the existence of the O-T phase boundary. Fig. 3(b) demonstrates the phase diagrams of the samples to observe the movement trend of the TO-T and TC directly. It can be seen that the doping of Liþ has a great influence on the TO-T and TC of the KNLxN-BNZ ceramics. The TC of all ceramics increased gradually with the addition of Liþ, and both have high values (>350 � C). The TO-T first shifts to low temperature and reaches a minimum of 58 � C when x ¼ 0.03, which has the highest coexistence proportion of O-T phase at room temperature.Then the TO-T rapidly increases when x ¼ 0.05, and the cause of this phenomenon has been reported in previous articles, partial Liþ ions are consumed in the secondary phase, resulting in the TO-T moving to the low temperature failing [26]. The TO-T of each component ceramic in the phase diagram is
2. Experimental procedure KNLxN-BNZ ceramic powders were synthesized using the traditional solid-state process. The materials were K2CO3 (99%), Na2CO3 (99.8%), Nb2O5 (99.5%), Li2CO3 (99%), Bi2O3 (99.9%), and ZrO2 (99%), with ethanol as the medium via a planetary ball mill for 24 h, then dried in 70 � C for10 h, and calcinated under 850 � C for 4 h after thoroghtly mixed the above powders. The pre-fired powders were mixed in a ball mill for 24 h, followed by mixing with a binder of PVA for granulation, and then isostatic compacted into pieces with a diameter of 13 mm and a thick ness of 1.3 mm under 10 MPa for 2 min. After the PVA was removed at 650 � C, these pieces were sintered at 1120 � C for 3 h. The sintered ceramic pieces were silvered at 600 � C on both sides. Finally, these ce ramics were polarized by applying a DC electric field of 3 kV/mm for 20–30 min in silicone oil at 100 � C. The phase composition of the ceramic samples was proved using a Xray diffraction (XRD, D/MAX 2500 PC). The Raman spectra in the range 100–1000 cm 1 were tested by a DXR Raman spectrometer (Thermo Scientific Nicolet, U.S.A.). The microstructure investigation of the ce ramics was performed and analyzed with field emission scanning elec tron microscopy (SEM, S-4800). The grain size distribution and average grain size of the samples was calculated using software (Nano Measurer). The dielectric properties and the εr-T curves of the samples were tested by an LCR Meter (4425) at 1 kHz. Piezoelectric constant (d33) of the samples was evaluated by the quasi-static d33 m (LC2730A). 3. Results and discussion Fig. 1(a) demonstrates the XRD diagrams of KNLxN-BNZ piezoelec tric ceramics sintered at 1120 � C. It was apparent that the specimens with the x below 0.05 exhibited a typical single perovskite structure, confirming that there was a homogeneous solid solution between K0.48Na0.52NbO3–Bi0.5Na0.5ZrO3 (KNN-BNZ) and Liþ. With the x increasing to 0.05, a secondary phase was observed in the pattern. Different articles [26,27] reported an identical secondary phase as K3Li2Nb5O15, which was also confirmed in the XRD results of the cor responding sample by phase retrieval using Jade software. The appearance of K3Li2Nb5O15 may be detrimental to the electrical prop erties of the ceramic. For further observation of the phase composition of the ceramics, the enlarged XRD diagrams with 2θ ¼ 44.5� –46.5� are plotted in Fig. 1(b). Previous studies [7] have shown that the phase composition of the KNN ceramics can be identified by the intensity variations of the (002) and (200) peaks in the XRD pattern. Fig. 1(b) clearly shows that the intensity contrast between the (002) and (200) peak variations is significant with the increase of Liþ. It can be inferred 2
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Materials Chemistry and Physics 245 (2020) 122806
Fig. 2. (a) Raman spectra of the ceramics with a function of x; (b) Vibration mode of ν1 and ν5; (c) Raman shift of ν1 and ν5 mode with the variation of x; (d) The function of the “c” and c/a with x.
Fig. 3. (a) εr-T curves of KNLxN-BNZ ceramics measured at 1 kHz; (b) Phase diagram of the KNLxN-BNZ ceramics.
consistent with the (002) and (200) peak intensity changes previously analyzed by XRD, which also validates the previous results. Fig. 4(a)-(e) shows the SEM images of KNLxN-BNZ ceramics sintered at 1120 � C. All the grains grow well, and the grain size of different ce ramics has changed significantly. The grain size of each grain in the image is calculated by the analysis software (Nano Measurer), and the grain size distribution are plotted as shown in Fig. 4(a)-(e). Fig. 4(f) demonstrates the variation of the average grain size of KNLxN-BNZ ce ramics. The average grain size increased to the maximum (~16.51 μm) at x ¼ 0.03 with the increase of Liþ, and then decreased at x ¼ 0.05. This indicated that proper doping of Liþ will effectively promote the growth of grains during the sintering process in air. In some aspects, in the ce ramics with larger grain size, the constraint of the domain wall on domain rotation is weakened, resulting in more polarization directions, and thus the piezoelectric properties is enhanced [2]. The implication is
that the maximum average grain size can also account for enhanced d33 when x ¼ 0.03. As x increased further to 0.05, the grain size decreased, which may be the production of the secondary phase hindering the growth of grains. Fig. 5(a) demonstrates the function of the εr and tanδ with x, measured at 1 kHz and room temperature. The εr tends to increase first and then decreases as x increases. The tanδ presented an opposite trend and teeny value of all ceramics. It exhibits the optimal dielectric prop erties of εr ¼ 1344 and tanδ ¼ 0.036 at x ¼ 0.03, which interestingly has the highest coexistence proportion of O-T phase. Fig. 5(b) represents the d33 as a function of x. As the concentration of Liþ increases, the d33 first increases and then decreases, where the d33 reach the optimal value (d33 ¼ 252 pC/N) when x ¼ 0.03, and afterwards they decrease significantly when x ¼ 0.05. This result is also in agreement with the larger grain size having better piezoelectric properties in the SEM. Studies have indicated 3
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Materials Chemistry and Physics 245 (2020) 122806
Fig. 4. SEM images of the KNLxN-BNZ ceramics with (a), x ¼ 0.00; (b), x ¼ 0.01; (c), x ¼ 0.02; (d), x ¼ 0.03, (e), x ¼ 0.05; (f), Average grain-size of the KNLxNBNZ ceramics.
Fig. 5. (a) Function of the εr and tanδ with x, measured at 1 kHz and room temperature. (b) Variation of d33 and kp values of ceramics.
that the T-phase has 6 spontaneous polarization directions along the <001>, while the O-phase has 12 spontaneous polarization directions along the <110> [31]. More spontaneous polarization directions are generated when the O-T phase coexists [32]. There are more sponta neous polarization directions in the ceramic, which facilitates the rota tion of the domain and greatly increases the piezoelectric activity. Therefore, the d33 of all component ceramic samples has a higher improvement than the pure single O-phase KNN ceramic (d33 ¼ 80 pC/N). In addition, the coexistence proportion of O-T phase is higher when x ¼ 0.03, and the more spontaneous polarization is favorable for the improvement of electrical performance. When x ¼ 0.05, the sec ondary phase hinders the movement of TO-T to low temperature, and the coexistence ratio of the O-T phase decreases, resulting in deterioration of piezoelectric performance.
have a certain contribution to enhanced piezoelectric performance. A higher coexistence of O-T phase fraction and larger grain size in KNL0.03N-BNZ ceramic showed the excellent performance for d33 ¼ 252 pC/N, and TC ¼ 382 � C, which is superior to these reported KNN-based piezoelectric materials, as presented in Table 1. This system had great guiding significance for the research of lead-free piezoceramics in hightemperature applications. Declaration of competing interest We declare that we have no financial and personal relationships with Table 1 d33 and TC of KNN-based ceramics.
4. Conclusions In this paper, a system of ceramics with O-T phase boundary was successfully synthesized by Liþ doped KNN-BNZ lead-free ceramics. The results show that the TO-T shift to low temperature and further control of the proportion of O-T phase coexistence is regulated by controlling the doping of Liþ. In addition, appropriate addition concentration of Liþ ions was found to promote the growth of grains, and larger crystal grains 4
Material composition
d33 (pC/N)
TC (� C)
Ref
KNBNZ KNN-LT-NS KNLNS-BZ KNN-BA (KNLNCZ)-x-y KNN-BS KNN-KCT-BM KNNS-CZ KNLN-BNZ
161 233 235 202 216 210 208 237 252
~370 ~290 ~267 ~370 ~365 ~340 ~335 ~290 ~382
[33] [34] [35] [36] [37] [38] [39] [24] This work
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Materials Chemistry and Physics 245 (2020) 122806
other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.
[19] N. Klein, E. Hollenstein, D. Damjanovic, H.J. Trodahl, N. Setter, M. Kuball, A study of the phase diagram of (K,Na,Li)NbO3 determined by dielectric and piezoelectric measurements, and Raman spectroscopy, J. Appl. Phys. 102 (2007), 014112. [20] W. Wang, X. Yuan, C. Ma, F. Tang, F. Wang, Y. Cao, Investigation on the phase transition behavior and electrical properties of textured Lix(K0.48Na0.52)1-xNbO3 piezoelectric ceramics, Ceram. Int. 41 (2015) 8377–8381. [21] H.T. Li, B.P. Zhang, P.P. Shang, Y. Fan, Q. Zhang, Phase Transition and high piezoelectric properties of Li0.058(Na0.52þxK0.48)0.942NbO3 lead-free ceramics, J. Am. Ceram. Soc. 94 (2011) 628–632. [22] Y.M. Li, Z.Y. Shen, L. J, F. Wu, Z.M. Wang, Y. Hong, R.H. Liao, Microstructure, phase transition and electrical propertiesof LiSbO3-doped (K0.49Na0.51)NbO3 leadfree piezoelectric ceramics, J. Mater. Sci. Mater. Electron. 41 (2012) 546–551. [23] L.M. Jiang, Y.Y. Li, J. Xing, J.G. Wu, Q. Chen, H. Liu, D.Q. Xiao, J.G. Zhu, Phase structure and enhanced piezoelectric properties in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05) O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 lead-free piezoelectric ceramics[J], Ceram. Int. 43 (2017) 2100–2106. [24] Z. Kong, W.F. Bai, P. Zheng, J.J. Zhang, F. Wen, D.Q. Chen, B. Shen, J.W. Zhai, Enhanced electromechanical properties of CaZrO3-modified (K0.5Na0.5)NbO3-based lead-free ceramics, Ceram. Int. 43 (2017) 7237–7242. [25] R.P. Xiang, J.G. Wu, Contribution of Bi0.5Na0.5ZrO3 on phase boundary and piezoelectricityin K0.48Na0.52Nb0.96Sb0.04O3-Bi0.5Na0.5SnO3-xBi0.5Na0.5ZrO3 ternary ceramics, J. Alloys Compd. 684 (2016) 397–402. [26] Z. Fu, J. Yang, P. Lu, L. Zhang, H. Yao, F. Xu, Y. Li, Influence of secondary phase on polymorphic phase transition in Li-doped KNN lead-free ceramics, Ceram. Int. 43 (2017) 12893–12897. [27] Y. Hou, C. Wang, J. Zhao, H. Ge, M. Zhu, H. Yan, The fine-grained KNN–LN ceramics densified from nanoparticles obtained by an economical sol–gel route, Mater. Chem. Phys. 134 (2012) 518–522. [28] X. Chen, X. Yan, X. Li, G. Liu, J. Sun, X. Li, H. Zhou, Excellent temperature stability on relative permittivity, and conductivity behavior of K0.5Na0.5NbO3 based lead free ceramics, J. Alloys Compd. 762 (2018) 697–705. [29] F. Rubio-Marcos, M.A. Banares, J.J. Romero, J.F. Fernandez, Correlation between the piezoelectric properties and the structure of lead-free KNN-modified ceramics, studied by Raman Spectroscopy, J. Raman Spectrosc. 42 (2011) 639–643. [30] L. Zhao, J. Gao, Q. Liu, S.J. Zhang, J.F. Li, Silver niobate lead-free antiferroelectric ceramics: enhancing energy storage density by B-site doping, Acs. Appl. Mater. Inter. 10 (2017) 819–826. [31] J.M. Guo, F. Xu, X.Z. Shang, Y.M. Lu, P. Li, T.S. Zhou, Z.L. Zhang, Y.B. He, Highperformance small-amount Fe2O3-doped (K,Na)NbO3-based lead-free piezoceramics with irregular phase evolution, J. Am. Ceram. 99 (2016) 2341–2346. [32] K. Higashide, K.I. Kakimoto, H. Ohsato, Temperature dependence on the piezoelectric property of (1 x)(Na0.5K0.5)NbO3-xLiNbO3 ceramics, J. Eur. Ceram. Soc. 27 (2007) 4107–4110. [33] X.P. Wang, J.G. Wu, X.J. Cheng, B.Y. Zhang, J.G. Zhu, D.Q. Xiao, Compositional dependence of phase structure and electrical properties in (K0.50Na0.50) 0.97Bi0.01(Nb1-xZrx)O3 lead-free ceramics, Ceram. Int. 39 (2013) 8021–8024. [34] H.W. Du, Y.Q. Huang, H.L. Li, H.P. Tang, W. Feng, Effects of NaSbO3 on phase structure and electrical properties of K0.5Na0.5NbO3-LiTaO3-NaSbO3 piezoelectric ceramics, J. Mater. Sci. Mater. Electron. 24 (3) (2012) 855–860. [35] B.Y. Zhang, X.P. Wang, X.J. Cheng, J.G. Zhu, D.Q. Xiao, J.G. Wu, Enhanced d33 value in (1-x)[(K0.50Na0.50)0.97Li0.03Nb0.97Sb0.03O3]-xBaZrO3 lead-free ceramics with an orthorhombic-rhombohedral phase boundary, J. Alloys Compd. 581 (2013) 446–451. [36] R.Z. Zuo, D.Y. Lv, J. Fu, Y. Liu, L.T. Li, Phase transition and electrical properties of lead free (Na0.5K0.5)NbO3-BiAlO3 ceramics, J. Alloys Compd. 476 (1–2) (2009) 836–839. [37] W.F. Liang, W.J. Wu, D.Q. Xiao, J.G. Zhu, Effect of the addition of CaZrO3 and LiNbO3 on the phase transitions and piezoelectric properties of K0.5Na0.5NbO3 leadfree ceramics, J. Am. Ceram. 94 (12) (2011) 4317–4322. [38] R.Z. Zuo, C. Ye, X.S. Fang, Dielectric and piezoelectric properties of Lead free Na0.5K0.5NbO3-BiScO3 ceramics, Jpn. J. Appl. Phys. 46 (2007) 6733–6736. [39] Y.B. Hu, X.Y. Liu, M.H. Jiang, X.W. Zhang, Phase structures and electrical properties of LiSbO3 doped 0.994K0.5Na0.5NbO3-0.004K5.4Cu1.3Ta10O290.002BiMnO3piezoelectric ceramics, J. Mater. Sci. 24 (1) (2013) 331–335.
Acknowledgements This work was supported by the Science and Technology Support Project of Hebei Province (Grant No. 15211111) and the National Nat ural Science Foundation of China (Grant No. 51502075). References [1] Y.C. Zhen, Z.Y. Cen, L.L. Chen, P.Y. Zhao, X.H. Wang, L.T. Li, The effect of microstructure on piezoelectric properties and temperature stability for MnO doped KNN-based ceramics sintered in different atmospheres, J. Alloys Compd. 752 (2018) 206–212. [2] Z. Wang, J.G. Wu, M. Xiao, D.Q. Xiao, T. Huang, B. Wu, F.X. Li, J.G. Zhu, Phase transition and electrical properties of (1-x)K0.5Na0.5NbO3–xBi0.5Na0.5Zr0.8Ti0.2O3 lead-free piezoceramics, Ceram. Int. 40 (2014) 9165–9169. [3] B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic Press, New York, 1971. [4] T. Zheng, J.G. Wu, X.J. Cheng, X.P. Wang, B.Y. Zhang, D.Q. Xiao, J.G. Zhu, X. J. Wang, X.J. Lou, High strain in (K0.40Na0.60)(Nb0.955Sb0.045)O3-Bi0.50Na0.50ZrO3 lead-free ceramics with large piezoelectricity, J. Mater. Chem. C. 2 (2014) 8796–8803. [5] J.G. Wu, Y.Y. Wang, D.Q. Xiao, J.G. Zhu, P. Yu, L. Wu, W.J. Wu, Piezoelectric properties of LiSbO3-Modified (K0.48Na0.52)NbO3 lead-free ceramics, Jpn. J. Appl. Phys. 46 (2007) 7375–7377. [6] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Lead-free piezoceramics, Nature 432 (2004) 84–87. [7] L.X. Xie, J. Xing, Z. Tan, L.M. Jiang, Q. Chen, J.G. Wu, W. Zhang, D.Q. Xiao, J. G. Zhu, Comprehensive investigation of structural and electrical properties of (Bi, Na)CoZrO3-doped KNN ceramics, J. Alloys Compd. 758 (2018) 14–24. [8] M.H. Zhang, K. Wang, Y.J. Du, G. Dai, W. Sun, G. Li, D. Hu, H.C. Thong, C.L. Zhao, X.Q. Xi, Z.X. Yue, J.F. Li, High and temperature-insensitive piezoelectric strain in alkali niobate lead-free Perovskite, J. Am. Ceram. Soc. 139 (2017) 3889–3895. [9] L.E. Cross, Electric double hysteresis in (KxNa1-x)NbO3 single crystals, Nature 181 (1958) 178–179. [10] G. Shirane, R. Newnham, R. Pepinsky, Dielectric properties and phase transitions of NaNbO3 and (Na,K)NbO3, Phys Rev 96 (1954) 581–588. [11] D.W. Baker, P.A. Thomas, N. Zhang, A.M. Glazer, A comprehensive study of the phase diagram of KxNa1-xNbO3, Appl. Phys. Lett. 95 (2009), 091903. [12] D. Lin, K.W. Kwok, H.L.W. Chan, Microstructure, phase transition, and electrical properties of (K0.5Na0.5)1 xLix(Nb1 yTay)O3 lead-free piezoelectric ceramics, J. Appl. Phys. 102 (2007), 034102. [13] Y. Zhang, L. Li, B. Shen, J. Zhai, Effect of orthorhombic–tetragonal phase transition on structure and piezoelectric properties of KNN-based lead-free ceramics, Dalton Trans. 44 (2015) 7797–7802. [14] Y.J. Dai, X.W. Zhang, G.Y. Zhou, Phase transitional behavior in K0.5Na0.5NbO3LiTaO3 ceramics, Appl. Phys. Lett. 90 (2007) 262903. [15] Y.J. Zhao, J.L. Liu, X.W. Zhang, H.P. Zhou, Domain switching mechanism of orthorhombic-tetragonal coexistence (Li,K,Na)NbO3, ceramics, J. Alloys Compd. 763 (2018) 695–700. [16] H. Fu, R.E. Cohen, Polarization rotation mechanism for ultra-high electromechanical response in single-crystal piezoelectrics, Nature 403 (2000) 281–283. [17] M. Ahart, M. Somayazulu, R.E. Cohen, P. Ganesh, P. Dera, H.K. Mao, R.J. Hemley, Y. Ren, P. Liermann, Z. Wu, Origin of morphotropic phase boundaries in ferroelectrics, Nature 451 (2008) 545–548. [18] Y. Guo, Ki Kakimoto, H. Ohsato, Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics, Appl. Phys. Lett. 85 (2004) 4121–4123.
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Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Phase structure regulation and enhanced piezoelectric properties of Li-doped KNN-based ceramics Rujie Zhao a, b, Yuanliang Li a, b, *, Zhanshen Zheng a, b, Wenshuo Kang a, b a
Key Lab of Environment Functional Materials of Tangshan City, 063210, Hebei, China Hebei Provincial Key Lab of Inorganic Nonmetallic Materials, College of Materials Science and Engineering, North China University of Science and Technology, Tangshan, 063210, Hebei, China
b
H I G H L I G H T S
� 0.96(K0.48Na0.52-xLix)NbO3-0.04Bi0.5Na0.5ZrO3(KNLxN-BNZ) ceramics was successfully synthesized. � The phase transition temperature TO-T and TC of the ceramics were shifted by Liþ doped. � KNL0.03N-BNZ ceramic has a lower TO-T and a higher coexistence proportion of O-T phase. � The highest proportion of two phases coexistence is the most efficient. � KNL0.03N-BNZ ceramic has a high TC while achieving high piezoelectric performance. A R T I C L E I N F O
A B S T R A C T
Keywords: Ceramics Phase transitions Raman spectroscopy Electrical properties
0.96(K0.48Na0.52-xLix)NbO3-0.04Bi0.5Na0.5ZrO3 (KNLxN-BNZ) lead-free ceramics have been synthesized by traditional solid-state reaction. Here, the relationship between phase composition and piezoelectric performance of ceramics is explored systematically. Analysis of XRD and Raman spectroscopy confirmed that the orthogonal (O) phase and the tetragonal (T) phase coexisted in each sample at room temperature. By studying the function curve of temperature and dielectric constant εr, it is found that the introduction of Liþ in ceramics can have a lower O-T phase transition temperature (TO-T) and a higher Curie temperature (TC), with the TO-T closest to room temperature and the highest coexistence volume proportion of O-T phase in the ceramic when x ¼ 0.03, which had the optimum values for d33 ¼ 252 pC/N and TC ¼ 382 � C. Due to the excellent piezoelectric properties and high TC, it is believed that KNLxN-BNZ piezoceramics can have great application prospects at high temperatures.
1. Introduction Piezoelectric ceramics are outstanding functional ceramics, mainly in the fields of transducers, actuators and sensors [1–4]. Lead-free piezoelectric ceramics are the ultimate development goal due to the sustainable development of human beings [5–8]. The KNN-based ((K, Na)NbO3) piezoelectric ceramics have become one of the research hot spot systems to replace PZT materials by its high TC, excellent piezo electric properties and ferroelectric properties [1,6–13]. However, compared with PZT ceramics, the comprehensive performance of KNN-based ceramics still needs further improvement. For KNN-based ceramics, the greatest concern is the establishment of a polycrystalline phase boundary at room temperature, just like the morphotropic phase boundary in PZT ceramics [8,14,15]. Due to the polycrystalline phases
coexisting, the spontaneous polarization directions in the ceramic in crease, the domain rotates easily under the external electric field, then the piezoelectric performance is enhanced [16,17]. Previous articles have reported that the pure KNN ceramic undergoes three phase tran sitions with temperature changes, and all phase transition temperatures of pure KNN ceramics are kept away from room temperature [7]. Studies have shown that the TO-T can be shifted by doping the second component in KNN ceramics, thus establishing an O-T phase boundary at room temperature. Liþ is one of them [18–20]. Especially, KNN ceramics modified by Li(NaK)NbO3 [21] or LiSbO3–KNN [22] exhibit a large d33 and high kp value due to the O-T phase boundary being established. In addition, compounds such as (Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 [23], CaZrO3 [24] and (Bi0.5Na0.5)ZrO3 [25] can be doped to control the phase composition of KNN ceramics and construct the
* Corresponding author. Key Lab of Environment Functional Materials of Tangshan City, 063210, Hebei, China. E-mail addresses: [email protected] (R. Zhao), [email protected] (Y. Li), [email protected] (Z. Zheng), [email protected] (W. Kang). https://doi.org/10.1016/j.matchemphys.2020.122806 Received 20 December 2019; Received in revised form 4 February 2020; Accepted 12 February 2020 Available online 13 February 2020 0254-0584/© 2020 Elsevier B.V. All rights reserved.
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rhombohedral-tetragonal(R-T) phase boundary, further optimizing the piezoelectric properties. When the components are located at the O-T or R-T phase boundary, the polarization direction of the ceramics can be more easily deflected between different symmetries, thus improving the piezoelectric properties. However, it is worth noting that some modified KNN ceramics mentioned above will be accompanied by a lower TC, which is not conducive to high-temperature applications. Therefore, it is necessary to realize large piezoelectricity and higher TC in KNN-based ceramics after modification. In this paper, a binary material system of KNLxN-BNZ piezoceramics with high TC was synthesized using the traditional sintering method. The evolution of crystal structure, grain size, multiphase coexistence behavior and piezoelectric performance of samples after doping of Liþ were studied. The structure of the O-T phase boundary was proved by XRD and Raman spectroscopy. In addition, the grain size and the phase transition temperature (TO-T and TC) of the KNLN-BNZ ceramics changed significantly with the doping of Liþ. Whereafter, the relationship be tween the coexistence proportion the of O-T phase and electrical per formance in ceramics was explored, and the internal mechanism was analyzed in depth.
Fig. 1. (a) XRD patterns of the KNLxN-BNZ ceramics; (b) Enlarged XRD pat terns in the range of 2θ from 44.5� to 46.5� .
that a phase transition has occurred in these ceramics, and all the ceramic samples were considered to possess an O-T phase boundary. The intensity ratio of the two peaks at x ¼ 0.03 is almost 1:1, indicating that the proportion of O-T phase coexisting in ceramics under this compo nent is the highest. There is an abnormal trend in the intensity variation of the two peaks at x ¼ 0.05, which may be due to the formation of K3Li2Nb5O15 affecting the transition of phase structure. To further confirm the results of the XRD analysis, Raman spectros copy in the range of 100–1000 cm 1 was performed on all ceramic samples, as shown in Fig. 2(a). All the vibration modes of NbO6, such as 1A1g(ν1)þ1Eg(ν2)þ2F1u(ν3,ν4)þF2g(ν5)þF2u(ν6) [28] were observed, where theν1 mode represents a symmetric stretching vibration of NbO6, which can determine the phase transition evolution [29] and ν5 repre sents a bending vibration mode of NbO6 [30], presented in Fig. 2(b). Fig. 2(c) demonstrates the variation of Raman shift with x of the A1g(ν1) and F2g(ν5) modes. It is observed that as the x increases to 0.03, the ν1 peak gradually shifts to a higher wave number and then decreases when x ¼ 0.05. The variation in Raman shift reflects the change in the distance between atoms in the oxygen octahedron or the variation in the chem ical bond angle between atoms. The reduction in Raman shift is accompanied by an increase in the spacing between atoms and vice versa. Fig. 2(d) shows the function of the refined cell parameter “c” and the crystal axis ratio c/a with the x content. The decrease of “c” indicates that the oxygen octahedron compressed along the direction of <001>, and the distance between the two oxygen atoms is reduced. The result was also consistent with the evolution of the ν1 peak in Fig. 2(c). The reason is that Liþ with smaller radius replaces the A-site of the KNN-BNZ ceramic, which leads to the fact that the crystal lattice of the KNN-BNZ ceramic as a whole exhibits the oxygen octahedron compression to the center and transforms into the T-phase. Anomalous changes in the Raman shift of the ν5 modes and the crystal axis ratio c/a further illus trate that the O-T phase exists in all samples. Fig. 3(a) demonstrates the εr-T curves of the KNLxN-BNZ ceramics, measured at 1 kHz. It can be observed that each of the εr-T curves has two obvious dielectric peaks corresponding to the TO-T and TC. For all ceramics, the TO-T (58 � C-107 � C) is close to room temperature, which proved the existence of the O-T phase boundary. Fig. 3(b) demonstrates the phase diagrams of the samples to observe the movement trend of the TO-T and TC directly. It can be seen that the doping of Liþ has a great influence on the TO-T and TC of the KNLxN-BNZ ceramics. The TC of all ceramics increased gradually with the addition of Liþ, and both have high values (>350 � C). The TO-T first shifts to low temperature and reaches a minimum of 58 � C when x ¼ 0.03, which has the highest coexistence proportion of O-T phase at room temperature.Then the TO-T rapidly increases when x ¼ 0.05, and the cause of this phenomenon has been reported in previous articles, partial Liþ ions are consumed in the secondary phase, resulting in the TO-T moving to the low temperature failing [26]. The TO-T of each component ceramic in the phase diagram is
2. Experimental procedure KNLxN-BNZ ceramic powders were synthesized using the traditional solid-state process. The materials were K2CO3 (99%), Na2CO3 (99.8%), Nb2O5 (99.5%), Li2CO3 (99%), Bi2O3 (99.9%), and ZrO2 (99%), with ethanol as the medium via a planetary ball mill for 24 h, then dried in 70 � C for10 h, and calcinated under 850 � C for 4 h after thoroghtly mixed the above powders. The pre-fired powders were mixed in a ball mill for 24 h, followed by mixing with a binder of PVA for granulation, and then isostatic compacted into pieces with a diameter of 13 mm and a thick ness of 1.3 mm under 10 MPa for 2 min. After the PVA was removed at 650 � C, these pieces were sintered at 1120 � C for 3 h. The sintered ceramic pieces were silvered at 600 � C on both sides. Finally, these ce ramics were polarized by applying a DC electric field of 3 kV/mm for 20–30 min in silicone oil at 100 � C. The phase composition of the ceramic samples was proved using a Xray diffraction (XRD, D/MAX 2500 PC). The Raman spectra in the range 100–1000 cm 1 were tested by a DXR Raman spectrometer (Thermo Scientific Nicolet, U.S.A.). The microstructure investigation of the ce ramics was performed and analyzed with field emission scanning elec tron microscopy (SEM, S-4800). The grain size distribution and average grain size of the samples was calculated using software (Nano Measurer). The dielectric properties and the εr-T curves of the samples were tested by an LCR Meter (4425) at 1 kHz. Piezoelectric constant (d33) of the samples was evaluated by the quasi-static d33 m (LC2730A). 3. Results and discussion Fig. 1(a) demonstrates the XRD diagrams of KNLxN-BNZ piezoelec tric ceramics sintered at 1120 � C. It was apparent that the specimens with the x below 0.05 exhibited a typical single perovskite structure, confirming that there was a homogeneous solid solution between K0.48Na0.52NbO3–Bi0.5Na0.5ZrO3 (KNN-BNZ) and Liþ. With the x increasing to 0.05, a secondary phase was observed in the pattern. Different articles [26,27] reported an identical secondary phase as K3Li2Nb5O15, which was also confirmed in the XRD results of the cor responding sample by phase retrieval using Jade software. The appearance of K3Li2Nb5O15 may be detrimental to the electrical prop erties of the ceramic. For further observation of the phase composition of the ceramics, the enlarged XRD diagrams with 2θ ¼ 44.5� –46.5� are plotted in Fig. 1(b). Previous studies [7] have shown that the phase composition of the KNN ceramics can be identified by the intensity variations of the (002) and (200) peaks in the XRD pattern. Fig. 1(b) clearly shows that the intensity contrast between the (002) and (200) peak variations is significant with the increase of Liþ. It can be inferred 2
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Fig. 2. (a) Raman spectra of the ceramics with a function of x; (b) Vibration mode of ν1 and ν5; (c) Raman shift of ν1 and ν5 mode with the variation of x; (d) The function of the “c” and c/a with x.
Fig. 3. (a) εr-T curves of KNLxN-BNZ ceramics measured at 1 kHz; (b) Phase diagram of the KNLxN-BNZ ceramics.
consistent with the (002) and (200) peak intensity changes previously analyzed by XRD, which also validates the previous results. Fig. 4(a)-(e) shows the SEM images of KNLxN-BNZ ceramics sintered at 1120 � C. All the grains grow well, and the grain size of different ce ramics has changed significantly. The grain size of each grain in the image is calculated by the analysis software (Nano Measurer), and the grain size distribution are plotted as shown in Fig. 4(a)-(e). Fig. 4(f) demonstrates the variation of the average grain size of KNLxN-BNZ ce ramics. The average grain size increased to the maximum (~16.51 μm) at x ¼ 0.03 with the increase of Liþ, and then decreased at x ¼ 0.05. This indicated that proper doping of Liþ will effectively promote the growth of grains during the sintering process in air. In some aspects, in the ce ramics with larger grain size, the constraint of the domain wall on domain rotation is weakened, resulting in more polarization directions, and thus the piezoelectric properties is enhanced [2]. The implication is
that the maximum average grain size can also account for enhanced d33 when x ¼ 0.03. As x increased further to 0.05, the grain size decreased, which may be the production of the secondary phase hindering the growth of grains. Fig. 5(a) demonstrates the function of the εr and tanδ with x, measured at 1 kHz and room temperature. The εr tends to increase first and then decreases as x increases. The tanδ presented an opposite trend and teeny value of all ceramics. It exhibits the optimal dielectric prop erties of εr ¼ 1344 and tanδ ¼ 0.036 at x ¼ 0.03, which interestingly has the highest coexistence proportion of O-T phase. Fig. 5(b) represents the d33 as a function of x. As the concentration of Liþ increases, the d33 first increases and then decreases, where the d33 reach the optimal value (d33 ¼ 252 pC/N) when x ¼ 0.03, and afterwards they decrease significantly when x ¼ 0.05. This result is also in agreement with the larger grain size having better piezoelectric properties in the SEM. Studies have indicated 3
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Fig. 4. SEM images of the KNLxN-BNZ ceramics with (a), x ¼ 0.00; (b), x ¼ 0.01; (c), x ¼ 0.02; (d), x ¼ 0.03, (e), x ¼ 0.05; (f), Average grain-size of the KNLxNBNZ ceramics.
Fig. 5. (a) Function of the εr and tanδ with x, measured at 1 kHz and room temperature. (b) Variation of d33 and kp values of ceramics.
that the T-phase has 6 spontaneous polarization directions along the <001>, while the O-phase has 12 spontaneous polarization directions along the <110> [31]. More spontaneous polarization directions are generated when the O-T phase coexists [32]. There are more sponta neous polarization directions in the ceramic, which facilitates the rota tion of the domain and greatly increases the piezoelectric activity. Therefore, the d33 of all component ceramic samples has a higher improvement than the pure single O-phase KNN ceramic (d33 ¼ 80 pC/N). In addition, the coexistence proportion of O-T phase is higher when x ¼ 0.03, and the more spontaneous polarization is favorable for the improvement of electrical performance. When x ¼ 0.05, the sec ondary phase hinders the movement of TO-T to low temperature, and the coexistence ratio of the O-T phase decreases, resulting in deterioration of piezoelectric performance.
have a certain contribution to enhanced piezoelectric performance. A higher coexistence of O-T phase fraction and larger grain size in KNL0.03N-BNZ ceramic showed the excellent performance for d33 ¼ 252 pC/N, and TC ¼ 382 � C, which is superior to these reported KNN-based piezoelectric materials, as presented in Table 1. This system had great guiding significance for the research of lead-free piezoceramics in hightemperature applications. Declaration of competing interest We declare that we have no financial and personal relationships with Table 1 d33 and TC of KNN-based ceramics.
4. Conclusions In this paper, a system of ceramics with O-T phase boundary was successfully synthesized by Liþ doped KNN-BNZ lead-free ceramics. The results show that the TO-T shift to low temperature and further control of the proportion of O-T phase coexistence is regulated by controlling the doping of Liþ. In addition, appropriate addition concentration of Liþ ions was found to promote the growth of grains, and larger crystal grains 4
Material composition
d33 (pC/N)
TC (� C)
Ref
KNBNZ KNN-LT-NS KNLNS-BZ KNN-BA (KNLNCZ)-x-y KNN-BS KNN-KCT-BM KNNS-CZ KNLN-BNZ
161 233 235 202 216 210 208 237 252
~370 ~290 ~267 ~370 ~365 ~340 ~335 ~290 ~382
[33] [34] [35] [36] [37] [38] [39] [24] This work
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other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.
[19] N. Klein, E. Hollenstein, D. Damjanovic, H.J. Trodahl, N. Setter, M. Kuball, A study of the phase diagram of (K,Na,Li)NbO3 determined by dielectric and piezoelectric measurements, and Raman spectroscopy, J. Appl. Phys. 102 (2007), 014112. [20] W. Wang, X. Yuan, C. Ma, F. Tang, F. Wang, Y. Cao, Investigation on the phase transition behavior and electrical properties of textured Lix(K0.48Na0.52)1-xNbO3 piezoelectric ceramics, Ceram. Int. 41 (2015) 8377–8381. [21] H.T. Li, B.P. Zhang, P.P. Shang, Y. Fan, Q. Zhang, Phase Transition and high piezoelectric properties of Li0.058(Na0.52þxK0.48)0.942NbO3 lead-free ceramics, J. Am. Ceram. Soc. 94 (2011) 628–632. [22] Y.M. Li, Z.Y. Shen, L. J, F. Wu, Z.M. Wang, Y. Hong, R.H. Liao, Microstructure, phase transition and electrical propertiesof LiSbO3-doped (K0.49Na0.51)NbO3 leadfree piezoelectric ceramics, J. Mater. Sci. Mater. Electron. 41 (2012) 546–551. [23] L.M. Jiang, Y.Y. Li, J. Xing, J.G. Wu, Q. Chen, H. Liu, D.Q. Xiao, J.G. Zhu, Phase structure and enhanced piezoelectric properties in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05) O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 lead-free piezoelectric ceramics[J], Ceram. Int. 43 (2017) 2100–2106. [24] Z. Kong, W.F. Bai, P. Zheng, J.J. Zhang, F. Wen, D.Q. Chen, B. Shen, J.W. Zhai, Enhanced electromechanical properties of CaZrO3-modified (K0.5Na0.5)NbO3-based lead-free ceramics, Ceram. Int. 43 (2017) 7237–7242. [25] R.P. Xiang, J.G. Wu, Contribution of Bi0.5Na0.5ZrO3 on phase boundary and piezoelectricityin K0.48Na0.52Nb0.96Sb0.04O3-Bi0.5Na0.5SnO3-xBi0.5Na0.5ZrO3 ternary ceramics, J. Alloys Compd. 684 (2016) 397–402. [26] Z. Fu, J. Yang, P. Lu, L. Zhang, H. Yao, F. Xu, Y. Li, Influence of secondary phase on polymorphic phase transition in Li-doped KNN lead-free ceramics, Ceram. Int. 43 (2017) 12893–12897. [27] Y. Hou, C. Wang, J. Zhao, H. Ge, M. Zhu, H. Yan, The fine-grained KNN–LN ceramics densified from nanoparticles obtained by an economical sol–gel route, Mater. Chem. Phys. 134 (2012) 518–522. [28] X. Chen, X. Yan, X. Li, G. Liu, J. Sun, X. Li, H. Zhou, Excellent temperature stability on relative permittivity, and conductivity behavior of K0.5Na0.5NbO3 based lead free ceramics, J. Alloys Compd. 762 (2018) 697–705. [29] F. Rubio-Marcos, M.A. Banares, J.J. Romero, J.F. Fernandez, Correlation between the piezoelectric properties and the structure of lead-free KNN-modified ceramics, studied by Raman Spectroscopy, J. Raman Spectrosc. 42 (2011) 639–643. [30] L. Zhao, J. Gao, Q. Liu, S.J. Zhang, J.F. Li, Silver niobate lead-free antiferroelectric ceramics: enhancing energy storage density by B-site doping, Acs. Appl. Mater. Inter. 10 (2017) 819–826. [31] J.M. Guo, F. Xu, X.Z. Shang, Y.M. Lu, P. Li, T.S. Zhou, Z.L. Zhang, Y.B. He, Highperformance small-amount Fe2O3-doped (K,Na)NbO3-based lead-free piezoceramics with irregular phase evolution, J. Am. Ceram. 99 (2016) 2341–2346. [32] K. Higashide, K.I. Kakimoto, H. Ohsato, Temperature dependence on the piezoelectric property of (1 x)(Na0.5K0.5)NbO3-xLiNbO3 ceramics, J. Eur. Ceram. Soc. 27 (2007) 4107–4110. [33] X.P. Wang, J.G. Wu, X.J. Cheng, B.Y. Zhang, J.G. Zhu, D.Q. Xiao, Compositional dependence of phase structure and electrical properties in (K0.50Na0.50) 0.97Bi0.01(Nb1-xZrx)O3 lead-free ceramics, Ceram. Int. 39 (2013) 8021–8024. [34] H.W. Du, Y.Q. Huang, H.L. Li, H.P. Tang, W. Feng, Effects of NaSbO3 on phase structure and electrical properties of K0.5Na0.5NbO3-LiTaO3-NaSbO3 piezoelectric ceramics, J. Mater. Sci. Mater. Electron. 24 (3) (2012) 855–860. [35] B.Y. Zhang, X.P. Wang, X.J. Cheng, J.G. Zhu, D.Q. Xiao, J.G. Wu, Enhanced d33 value in (1-x)[(K0.50Na0.50)0.97Li0.03Nb0.97Sb0.03O3]-xBaZrO3 lead-free ceramics with an orthorhombic-rhombohedral phase boundary, J. Alloys Compd. 581 (2013) 446–451. [36] R.Z. Zuo, D.Y. Lv, J. Fu, Y. Liu, L.T. Li, Phase transition and electrical properties of lead free (Na0.5K0.5)NbO3-BiAlO3 ceramics, J. Alloys Compd. 476 (1–2) (2009) 836–839. [37] W.F. Liang, W.J. Wu, D.Q. Xiao, J.G. Zhu, Effect of the addition of CaZrO3 and LiNbO3 on the phase transitions and piezoelectric properties of K0.5Na0.5NbO3 leadfree ceramics, J. Am. Ceram. 94 (12) (2011) 4317–4322. [38] R.Z. Zuo, C. Ye, X.S. Fang, Dielectric and piezoelectric properties of Lead free Na0.5K0.5NbO3-BiScO3 ceramics, Jpn. J. Appl. Phys. 46 (2007) 6733–6736. [39] Y.B. Hu, X.Y. Liu, M.H. Jiang, X.W. Zhang, Phase structures and electrical properties of LiSbO3 doped 0.994K0.5Na0.5NbO3-0.004K5.4Cu1.3Ta10O290.002BiMnO3piezoelectric ceramics, J. Mater. Sci. 24 (1) (2013) 331–335.
Acknowledgements This work was supported by the Science and Technology Support Project of Hebei Province (Grant No. 15211111) and the National Nat ural Science Foundation of China (Grant No. 51502075). References [1] Y.C. Zhen, Z.Y. Cen, L.L. Chen, P.Y. Zhao, X.H. Wang, L.T. Li, The effect of microstructure on piezoelectric properties and temperature stability for MnO doped KNN-based ceramics sintered in different atmospheres, J. Alloys Compd. 752 (2018) 206–212. [2] Z. Wang, J.G. Wu, M. Xiao, D.Q. Xiao, T. Huang, B. Wu, F.X. Li, J.G. Zhu, Phase transition and electrical properties of (1-x)K0.5Na0.5NbO3–xBi0.5Na0.5Zr0.8Ti0.2O3 lead-free piezoceramics, Ceram. Int. 40 (2014) 9165–9169. [3] B. Jaffe, W.R. Cook, H. Jaffe, Piezoelectric Ceramics, Academic Press, New York, 1971. [4] T. Zheng, J.G. Wu, X.J. Cheng, X.P. Wang, B.Y. Zhang, D.Q. Xiao, J.G. Zhu, X. J. Wang, X.J. Lou, High strain in (K0.40Na0.60)(Nb0.955Sb0.045)O3-Bi0.50Na0.50ZrO3 lead-free ceramics with large piezoelectricity, J. Mater. Chem. C. 2 (2014) 8796–8803. [5] J.G. Wu, Y.Y. Wang, D.Q. Xiao, J.G. Zhu, P. Yu, L. Wu, W.J. Wu, Piezoelectric properties of LiSbO3-Modified (K0.48Na0.52)NbO3 lead-free ceramics, Jpn. J. Appl. Phys. 46 (2007) 7375–7377. [6] Y. Saito, H. Takao, T. Tani, T. Nonoyama, K. Takatori, T. Homma, T. Nagaya, M. Nakamura, Lead-free piezoceramics, Nature 432 (2004) 84–87. [7] L.X. Xie, J. Xing, Z. Tan, L.M. Jiang, Q. Chen, J.G. Wu, W. Zhang, D.Q. Xiao, J. G. Zhu, Comprehensive investigation of structural and electrical properties of (Bi, Na)CoZrO3-doped KNN ceramics, J. Alloys Compd. 758 (2018) 14–24. [8] M.H. Zhang, K. Wang, Y.J. Du, G. Dai, W. Sun, G. Li, D. Hu, H.C. Thong, C.L. Zhao, X.Q. Xi, Z.X. Yue, J.F. Li, High and temperature-insensitive piezoelectric strain in alkali niobate lead-free Perovskite, J. Am. Ceram. Soc. 139 (2017) 3889–3895. [9] L.E. Cross, Electric double hysteresis in (KxNa1-x)NbO3 single crystals, Nature 181 (1958) 178–179. [10] G. Shirane, R. Newnham, R. Pepinsky, Dielectric properties and phase transitions of NaNbO3 and (Na,K)NbO3, Phys Rev 96 (1954) 581–588. [11] D.W. Baker, P.A. Thomas, N. Zhang, A.M. Glazer, A comprehensive study of the phase diagram of KxNa1-xNbO3, Appl. Phys. Lett. 95 (2009), 091903. [12] D. Lin, K.W. Kwok, H.L.W. Chan, Microstructure, phase transition, and electrical properties of (K0.5Na0.5)1 xLix(Nb1 yTay)O3 lead-free piezoelectric ceramics, J. Appl. Phys. 102 (2007), 034102. [13] Y. Zhang, L. Li, B. Shen, J. Zhai, Effect of orthorhombic–tetragonal phase transition on structure and piezoelectric properties of KNN-based lead-free ceramics, Dalton Trans. 44 (2015) 7797–7802. [14] Y.J. Dai, X.W. Zhang, G.Y. Zhou, Phase transitional behavior in K0.5Na0.5NbO3LiTaO3 ceramics, Appl. Phys. Lett. 90 (2007) 262903. [15] Y.J. Zhao, J.L. Liu, X.W. Zhang, H.P. Zhou, Domain switching mechanism of orthorhombic-tetragonal coexistence (Li,K,Na)NbO3, ceramics, J. Alloys Compd. 763 (2018) 695–700. [16] H. Fu, R.E. Cohen, Polarization rotation mechanism for ultra-high electromechanical response in single-crystal piezoelectrics, Nature 403 (2000) 281–283. [17] M. Ahart, M. Somayazulu, R.E. Cohen, P. Ganesh, P. Dera, H.K. Mao, R.J. Hemley, Y. Ren, P. Liermann, Z. Wu, Origin of morphotropic phase boundaries in ferroelectrics, Nature 451 (2008) 545–548. [18] Y. Guo, Ki Kakimoto, H. Ohsato, Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics, Appl. Phys. Lett. 85 (2004) 4121–4123.
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