[1] [1] LI Jingfeng, WANG Ke, ZHU Fangyuan, et al. (K,Na)NbO3-based lead-free piezoceramics: fundamental aspects, processing technologies, and remaining challenges [J]. Journal of the American Ceramic Society, 2013, 96(12): 3677-3696.

[3] [3] WU Jiagang, XIAO Dingquan, ZHU Jiaguo. Potassium-sodium niobate lead-free piezoelectric materials: Past, present, and future of phase boundaries [J]. Chemical Reviews, 2015, 115(7): 2559-2595.

[4] [4] SATIO Y, TAKAO H, TANI T, et al. Lead-free piezoceramics [J]. Nature, 2004, 432: 84-87.

[5] [5] LI Peng, ZHAI Jiwei, SHEN Bo, et al. Ultrahigh piezoelectric properties in textured (K,Na)NbO3-based lead-free ceramics [J]. Advanced Materials, 2018, 30(8): 1705171.

[6] [6] GUO Yiping, KAKIMOTO Ki, OHSATO H. Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3-LiNbO3 ceramics [J]. Applied Physics Letters, 2004, 85(18): 4121-4123.

[7] [7] WANG Ke, LI Jingfeng. Domain engineering of lead-free Li-modified (K,Na)NbO3 polycrystals with highly enhanced piezoelectricity [J]. Advanced Functional Materials, 2010, 20(12): 1924-1929.

[8] [8] RDEL J, WEBBER K G, DITTMER R, et al. Transferring lead-free piezoelectric ceramics into application [J]. Journal of the European Ceramic Society, 2015, 35(6): 1659-1681.

[9] [9] LIU Huan, LIU Yixuan, SONG Aizhen, et al. (K, Na)NbO3-based lead-free piezoceramics: One more step to boost applications [J]. National Science Review, 2022, 9:1-3.

[11] [11] WANG Ke, LI Jingfeng. Analysis of crystallographic evolution in (Na,K)NbO3-based lead-free piezoceramics by X-ray diffraction [J]. Applied Physics Letters, 2007, 91(26): 262902.

[13] [13] SHROUT T R, ZHANG S J. Lead-free piezoelectric ceramics: Alternatives for PZT [J]. Journal of Electroceramics, 2007, 19(1):113-126.

[14] [14] WU L, ZHANG J L, WANG C L. Influence of compositional ratio K/Na on physical properties in (KxNa1-x)NbO3 ceramics [J]. Journal of Applied Physics, 2008, 103(8): 084116.