[1] [1] RDEL J, LI J F. Lead-free piezoceramics: Status and perspectives[J]. MRS Bull, 2018, 43(8): 576–580.

[2] [2] JAFFE B, COOK W R JR, JAFFE H. The piezoelectric effect in ceramics[J]. Piezoelectric Ceram, 1971: 7–21.

[3] [3] SETTER N. Piezoelectric materials in devices[M]. S.l.: s.n., 2002.

[4] [4] THONG H C, ZHAO C L, ZHOU Z, et al. Technology transfer of lead-free (K, Na)NbO3-based piezoelectric ceramics[J]. Mater Today, 2019, 29: 37–48.

[5] [5] KORUZA J, BELL A J, FRMLING T, et al. Requirements for the transfer of lead-free piezoceramics into application[J]. J Materiomics, 2018, 4(1): 13–26.

[6] [6] HAERTLING G H. Ferroelectric ceramics: history and technology[J]. J Am Ceram Soc, 1999, 82(4): 797–818.

[7] [7] WU Y Q, SOON P S, LU J T, et al. Life cycle assessment of lead-free potassium sodium niobate versus lead zirconate titanate: Energy and environmental impacts[J]. EcoMat, 2024, 6(5): e12450.

[8] [8] LIU H, LIU Y X, SONG A Z, et al. (K, Na)NbO3-based lead-free piezoceramics: One more step to boost applications[J]. Natl Sci Rev, 2022, 9(8): nwac101.

[9] [9] BELL A J, DEUBZER O. Lead-free piezoelectrics—The environmental and regulatory issues[J]. MRS Bull, 2018, 43(8): 581–587.

[10] [10] ZHANG Y C, LI J F. Review of chemical modification on potassium sodium niobate lead-free piezoelectrics[J]. J Mater Chem C, 2019, 7(15): 4284–4303.

[11] [11] WU J G, XIAO D Q, ZHU J G. Potassium-sodium niobate lead-free piezoelectric materials: Past, present, and future of phase boundaries[J]. Chem Rev, 2015, 115(7): 2559–2595.

[12] [12] SHROUT T R, ZHANG S J. Lead-free piezoelectric ceramics: Alternatives for PZT?[J]. J Electroceram, 2007, 19(1): 113–126.

[13] [13] LIU Q, ZHANG Y C, GAO J, et al. High-performance lead-free piezoelectrics with local structural heterogeneity[J]. Energy Environ Sci, 2018, 11(12): 3531–3539.

[14] [14] LIU Q, ZHANG Y C, GAO J, et al. Practical high-performance lead-free piezoelectrics: Structural flexibility beyond utilizing multiphase coexistence[J]. Natl Sci Rev, 2020, 7(2): 355–365.

[15] [15] LIU X M, TAN X L. Giant strains in non-textured (Bi1/2Na1/2)TiO3-based lead-free ceramics[J]. Adv Mater, 2016, 28(3): 574–578.

[16] [16] RDEL J, JO W, SEIFERT K T P, et al. Perspective on the development of lead-free piezoceramics[J]. J Am Ceram Soc, 2009, 92(6): 1153–1177.

[17] [17] RAHAMAN M N. Ceramic Processing and Sintering[M]. S.l.: CRC Press, 2017.

[18] [18] BERNACHE-ASSOLLANT D. Chimie physique du frittage[M]. Hermes, 1993.

[19] [19] MALIC B, BENCAN A, ROJAC T, et al. Lead-free piezoelectrics based on alkaline niobates: Synthesis, sintering and microstructure[J]. Acta Chim Slov, 2008, 55(4): 719–726.

[20] [20] ACKER J, KUNGL H, HOFFMANN M J. Influence of alkaline and niobium excess on sintering and microstructure of sodium-potassium niobate (K0.5 Na0.5)NbO3[J]. J Am Ceram Soc, 2010, 93(5): 1270–1281.

[21] [21] WANG Y L, DAMJANOVIC D, KLEIN N, et al. Compositional inhomogeneity in Li- and Ta-modified (K, Na)NbO3 ceramics[J]. J Am Ceram Soc, 2007, 90(11): 3485–3489.

[22] [22] ROJAC T, BENAN A, URI H, et al. Synthesis of a Li- and Ta-modified (K, Na)NbO3 solid solution by mechanochemical activation[J]. J Am Ceram Soc, 2008, 91(11): 3789–3791.

[23] [23] KINGERY W D, BOWEN H K, UHLMANN D R. Introduction to ceramics[M]. John Wiley & Sons, 1976.

[24] [24] MALI B, KORUZA J, HREAK J, et al. Sintering of lead-free piezoelectric sodium potassium niobate ceramics[J]. Materials, 2015, 8(12): 8117–8146.

[25] [25] KORUZA J, MALI B. Initial stage sintering mechanism of NaNbO3 and implications regarding the densification of alkaline niobates[J]. J Eur Ceram Soc, 2014, 34(8): 1971–1979.

[26] [26] GERMAN R M. Sintering theory and practice[M]. New York: Wiley, 1996.

[27] [27] MALIC B, JENKO D, BERNARD J, et al. Synthesis and sintering of (K, Na)NbO3 based ceramics[J]. MRS Online Proc Libr, 2003, 755(1): 44.

[28] [28] JENKO D, BENCAN A, MALIC B, et al. Electron microscopy studies of potassium sodium niobate ceramics[J]. Microsc Microanal, 2005, 11(6): 572–580.

[29] [29] MADARO F, STERLI R, TOLCHARD J R, et al. Molten salt synthesis of K4Nb6O17, K2Nb4O11 and KNb3O8 crystals with needle- or plate-like morphology[J]. Cryst Eng Comm, 2011, 13(5): 1304–1313.

[30] [30] BIESUZ M, GRASSO S, SGLAVO V M. What’s new in ceramics sintering? A short report on the latest trends and future prospects[J]. Curr Opin Solid State Mater Sci, 2020, 24(5): 100868.

[31] [31] JAEGER R E, EGERTON L. Hot pressing of potassium-sodium niobates[J]. J Am Ceram Soc, 1962, 45(5): 209–213.

[32] [32] ZHANG J L, JI P F, WU Y Q, et al. Strong piezoelectricity exhibited by large-grained BaTiO3 ceramics[J]. Appl Phys Lett, 2014, 104(22): 222909.

[33] [33] LIU Y X, THONG H C, CHENG Y Y S, et al. Defect-mediated domain-wall motion and enhanced electric-field-induced strain in hot-pressed K0.5Na0.5NbO3 lead-free piezoelectric ceramics[J]. J Appl Phys, 2021, 129(2): 024102.

[34] [34] LI J F, WANG S N, WAKABAYASHI K, et al. Properties of modified lead zirconate titanate ceramics prepared at low temperature (800℃) by hot isostatic pressing[J]. J Am Ceram Soc, 2000, 83(4): 955–957.

[35] [35] LIU K, WANG W, LIU Q, et al. Photostriction properties of PLZT (4/52/48) ceramics sintered by SPS[J]. Ceram Inter, 2019, 45(2): 2097–2102.

[36] [36] NIE L T, HE X Y, CHANG C K, et al. Effect of anisotropy on the ferroelectric, optical, and electro-optic properties of PLZT transparent ceramics prepared by uniaxial hot-press sintering techniques[J]. Opt Mater Express, 2016, 6(11): 3565.

[37] [37] ZHANG Z, YAN H X, XIANG P H, et al. Grain orientation effects on the properties of a bismuth layer-structured ferroelectric (BLSF) Bi3NbTiO9 solid solution[J]. J Am Ceram Soc, 2004, 87(4): 602–605.

[38] [38] WOLLASTON W H. I. The Bakerian Lecture.—On a method of rendering platina malleable[J]. Phil Trans R Soc, 1829, 119: 1–8.

[39] [39] KANG W S, GUO X J, ZHOU Z Y, et al. Enhanced resistivity and strain stability of BiFeO3–BaTiO3 ceramics by hot-press sintering in oxygen atmosphere[J]. J Am Ceram Soc, 2023, 106(10): 5846–5854.

[40] [40] LI Z X, SUN H J, LIU X F, et al. High performance lead-free Na0.5K0.5NbO3 piezoelectric ceramics obtained via oscillatory hot-pressing[J]. Ceram Int, 2020, 46(8): 11617–11621.

[41] [41] XIE Z P, LI S, AN L N. A novel oscillatory pressure-assisted hot pressing for preparation of high-performance ceramics[J]. J Am Ceram Soc, 2014, 97(4): 1012–1015.

[42] [42] BOCANEGRA-BERNAL M H. Hot Isostatic Pressing (HIP) technology and its applications to metals and ceramics[J]. J Mater Sci, 2004, 39(21): 6399–6420.

[43] [43] ZIEGLER G, HEINRICH J, WTTING G. Relationships between processing, microstructure and properties of dense and reaction-bonded silicon nitride[J]. J Mater Sci, 1987, 22(9): 3041–3086.

[44] [44] ZIMMERMAN F. Isostatic pressing offers production advantages for complex shapes[J]. Ceram Ind, 1998, 148(3): 33–37.

[45] [45] WANG S N, LI J F, WAKABAYASHI K, et al. Lost silicon mold process for PZT microstructures[J]. Adv Mater, 1999, 11(10): 873–876.

[46] [46] MORGAN W R, SANDS R L. Isostatic compaction of metal powders[J]. Metall Rev, 1969, 14(1): 85–102.

[47] [47] ATKINSON H, RICKINSON B. The Adam Hilger Series on New Manufacturing Processes and Materials[J]. Hot Isostatic Proc, 1991: 1–71.

[48] [48] Heinrich J, Bohmer M. Microstructure and mechanical properties of hot-isostatic-pressed silicon nitride[C]//Proc. 11 th International Conf. on Science of Ceramics held at Stenungsund, Sweden, June 14-17, 1981: 439.

[49] [49] GUILLON O, GONZALEZ-JULIAN J, DARGATZ B, et al. Field-assisted sintering technology/spark plasma sintering: Mechanisms, materials, and technology developments[J]. Adv Eng Mater, 2014, 16(7): 830–849.

[50] [50] MUNIR Z A, ANSELMI-TAMBURINI U, OHYANAGI M. The effect of electric field and pressure on the synthesis and consolidation of materials: A review of the spark plasma sintering method[J]. J Mater Sci, 2006, 41(3): 763–777.

[51] [51] MUNIR Z A, QUACH D V, OHYANAGI M. Electric field and current effects on sintering[M]//Engineering Materials. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012: 137–158.

[52] [52] SUAREZ M, FERNANDEZ A, MENENDEZ J L, et al. Challenges and opportunities for spark plasma sintering: A key technology for a new generation of materials[J]. Sinter Appli, 2013, 13: 319–342.

[53] [53] MCWILLIAMS B, ZAVALIANGOS A. Multi-phenomena simulation of electric field assisted sintering[J]. J Mater Sci, 2008, 43(14): 5031–5035.

[54] [54] SCHWESIG D, SCHIERNING G, THEISSMANN R, et al. From nanoparticles to nanocrystalline bulk: Percolation effects in field assisted sintering of silicon nanoparticles[J]. Nanotechnology, 2011, 22(13): 135601.

[55] [55] ANGERER P, YU L G, KHOR K A, et al. Spark-plasma-sintering (SPS) of nanostructured titanium carbonitride powders[J]. J Eur Ceram Soc, 2005, 25(11): 1919–1927.

[56] [56] LANGER J, QUACH D V, GROZA J R, et al. A comparison between FAST and SPS apparatuses based on the sintering of oxide ceramics[J]. Int J Appl Ceram Technol, 2011, 8(6): 1459–1467.

[57] [57] KOSEC M, KOLAR D. On activated sintering and electrical properties of NaKNbO3[J]. Mater Res Bull, 1975, 10(5): 335–339.

[58] [58] MALIC B, BERNARD J, HOLC J, et al. Alkaline-earth doping in (K, Na)NbO3 based piezoceramics[J]. J Eur Ceram Soc, 2005, 25(12): 2707–2711.

[59] [59] VENDRELL X, GARCA J E, BRIL X, et al. Improving the functional properties of (K0.5Na0.5)NbO3 piezoceramics by acceptor doping[J]. J Eur Ceram Soc, 2015, 35(1): 125–130.

[60] [60] WANG K, LI J F. Low-temperature sintering of Li-modified (K, Na)NbO3 lead-free ceramics: Sintering behavior, microstructure, and electrical properties[J]. J Am Ceram Soc, 2010, 93(4): 1101–1107.

[61] [61] BANNO H. Effects of shape and volume fraction of closed pores on dielectric, elastic, and electromechanical properties of dielectric and piezoelectric ceramics: A theoretical approach[J]. Am Ceram Soc Bull, 1987, 66(9): 1332–1337.

[62] [62] LI J F, ZHEN Y H, ZHANG B P, et al. Normal sintering of (K, Na)NbO3-based lead-free piezoelectric ceramics[J]. Ceram Int, 2008, 34(4): 783–786.

[63] [63] LIU C, LIU P, KOBAYASHI K, et al. Enhancement of piezoelectric performance of lead-free NKN-based ceramics via a high-performance flux—NaF–Nb2O5[J]. J Am Ceram Soc, 2013, 96(10): 3120–3126.

[64] [64] BIROL H, DAMJANOVIC D, SETTER N. Preparation and characterization of (K0.5Na0.5)NbO3 ceramics[J]. J Eur Ceram Soc, 2006, 26(6): 861–866.

[65] [65] LIU X, CHEN X M, LIU M D, et al. Improved dielectric and ferroelectric properties of fine-grained K0.5Na0.5NbO3 ceramics via hot-press sintering[J]. Ceram Int, 2022, 48(8): 11615–11622.

[66] [66] HAERTLING G H. Properties of hot-pressed ferroelectric alkali niobate ceramics[J]. J Am Ceram Soc, 1967, 50(6): 329–330.

[67] [67] Bahanurdin F K, Mohamed J J, Ahmad Z A. Effect of Sintering Temperature on Structure and Dielectric Properties of Lead Free K0.5Na0.5NbO3 Prepared via Hot Isostatic Pressing[C]//Materials Science Forum. Trans Tech Publications Ltd, 2017, 888: 42–46.

[68] [68] LI J F, WANG K, ZHANG B P, et al. Ferroelectric and piezoelectric properties of fine-grained Na0.5K0.5NbO3 lead-free piezoelectric ceramics prepared by spark plasma sintering[J]. J Am Ceram Soc, 2006, 89(2): 706–709.

[69] [69] BAH M, GIOVANNELLI F, SCHOENSTEIN F, et al. High electromechanical performance with spark plasma sintering of undoped K0.5Na0.5NbO3 ceramics[J]. Ceram Int, 2014, 40(5): 7473–7480.

[70] [70] CARROLL M M, HOLT A C. Static and dynamic pore-collapse relations for ductile porous materials[J]. J Appl Phys, 1972, 43(4): 1626–1636.

[71] [71] ZHANG B P, LI J F, WANG K, et al. Compositional dependence of piezoelectric properties in NaxK1–xNbO3 lead-free ceramics prepared by spark plasma sintering[J]. J Am Ceram Soc, 2006, 89(5): 1605–1609.

[72] [72] MAIWA H. Dielectric and electromechanical properties of (K, Na)NbO3 Ceramics prepared by hot isostatic pressing[J]. Ferroelectrics, 2016, 491(1): 71–78.

[73] [73] HREAK J, BENCAN A, ROJAC T, et al. The influence of different niobium pentoxide precursors on the solid-state synthesis of potassium sodium niobate[J]. J Eur Ceram Soc, 2013, 33(15/16): 3065–3075.

[74] [74] MOURE A, CASTRO A, PARDO L. Improvement by recrystallisation of Aurivillius-type structure piezoceramics from mechanically activated precursors[J]. Acta Mater, 2004, 52(4): 945–957.

[75] [75] ZHU W, SHEN Z Y, DENG W, et al. A review: (Bi, Na)TiO3 (BNT)-based energy storage ceramics[J]. J Materiomics, 2024, 10(1): 86–123.

[76] [76] PARDO L, CASTRO A, MILLN P, et al. (Bi3TiNbO9)x(SrBi2Nb2O9)1–x aurivillius type structure piezoelectric ceramics obtained from mechanochemically activated oxides[J]. Acta Mater, 2000, 48(9): 2421–2428.

[77] [77] ZHENG P, ZHANG J L, TAN Y Q, et al. Grain-size effects on dielectric and piezoelectric properties of poled BaTiO3 ceramics[J]. Acta Mater, 2012, 60(13/14): 5022–5030.

[78] [78] HIRUMA Y, AOYAGI R, NAGATA H, et al. Piezoelectric properties of BaTiO3–(Bi1/2K1/2)TiO3 ferroelectric ceramics[J]. Jpn J Appl Phys, 2004, 43(11A): 7556–7559.

[79] [79] BUSCAGLIA V, BUSCAGLIA M T, VIVIANI M, et al. Grain size and grain boundary-related effects on the properties of nanocrystalline Barium titanate ceramics[J]. J Eur Ceram Soc, 2006, 26(14): 2889–2898.

[80] [80] MOURE A, CASTRO A, PARDO L. Aurivillius-type ceramics, a class of high temperature piezoelectric materials: Drawbacks, advantages and trends[J]. Prog Solid State Chem, 2009, 37(1): 15–39.

[81] [81] EPHERRE R, LESSEUR J, ALBINO M, et al. Adjustable dielectric properties of BaTiO3 containing MgO inclusions deformable under Spark Plasma Sintering[J]. Scr Mater, 2016, 110: 82–86.

[82] [82] MAIWA H. Piezoelectric properties of BaTiO3 ceramics prepared by hot isostatic pressing[J]. J Ceram Soc Jpn, 2013, 121(1416): 655–658.

[83] [83] HIRATA Y, NITTA A, SAMESHIMA S, et al. Dielectric properties of Barium titanate prepared by hot isostatic pressing[J]. Mater Lett, 1996, 29(4–6): 229–234.

[84] [84] DENG X Y, WANG X H, WEN H, et al. Phase transitions in nanocrystalline Barium titanate ceramics prepared by spark plasma sintering[J]. J Am Ceram Soc, 2006, 89(3): 1059–1064.

[85] [85] Ewsuk K G, Messing G L. Isostatic Hot Pressing of Sintered Lead Zirconate Titanate[C]//Proceedings of the 5th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings. Hoboken, NJ, USA: John Wiley & Sons, Inc., 1981, 2: 450–455.

[86] [86] RANDALL C A, KIM N, KUCERA J P, et al. Intrinsic and extrinsic size effects in fine-grained morphotropic-phase-boundary lead zirconate titanate ceramics[J]. J Am Ceram Soc, 1998, 81(3): 677–688.

[87] [87] LIU Y X, THONG H C, ZHAO C L, et al. Influence of trace zirconia addition on the properties of (K, Na)NbO3 solid solutions[J]. J Mater Chem C, 2019, 7(23): 6914–6923.

[88] [88] ARLT G, HENNINGS D, DE WITH G. Dielectric properties of fine-grained Barium titanate ceramics[J]. J Appl Phys, 1985, 58(4): 1619–1625.

[89] [89] WANG W, HE J Y, SUN Q F, et al. Enhanced piezoelectric properties and temperature stability of 0.5BZT-0.5BCT ceramic induced by using three-step synthesizing method[J]. ECS J Solid State Sci Technol, 2019, 8(9): N134–N139.

[90] [90] MARTIRENA H T, BURFOOT J C. Grain-size and pressure effects on the dielectric and piezoelectric properties of hot-pressed PZT-5[J]. Ferroelectrics, 1974, 7(1): 151–152.

[91] [91] YANG W W, LI P, WU S H, et al. A study on the relationship between grain size and electrical properties in (K,Na)NbO3-based lead-free piezoelectric ceramics[J]. Adv Elect Mater, 2019, 5(12): 1900570.

[92] [92] MAIWA H. Dielectric and electromechanical properties of BaTiO3 ceramics prepared by hot isostatic pressing[J]. Ferroelectrics, 2014, 463(1): 15–24.

[93] [93] EWSUK K G, MESSING G L. Densification of sintered lead zirconate titanate by hot isostatic pressing[J]. J Mater Sci, 1984, 19(5): 1530–1534.

[94] [94] LUAN W L, GAO L, KAWAOKA H, et al. Fabrication and characteristics of fine-grained BaTiO3 ceramics by spark plasma sintering[J]. Ceram Int, 2004, 30(3): 405–410.

[95] [95] WU Y J, LI J, KIMURA R, et al. Effects of preparation conditions on the structural and optical properties of spark plasma-sintered PLZT (8/65/35) ceramics[J]. J Am Ceram Soc, 2005, 88(12): 3327–3331.

[96] [96] NIEMIEC P, BOCHENEK D, BRZEZISKA D. Effect of various sintering methods on the properties of PZT-type ceramics[J]. Ceram Int, 2023, 49(22): 35687–35698.

[97] [97] SHEN Z Y, LI J F, WANG K, et al. Electrical and mechanical properties of fine-grained Li/Ta-modified (Na, K)NbO3-based piezoceramics prepared by spark plasma sintering[J]. J Am Ceram Soc, 2010, 93(5): 1378–1383.

[98] [98] ZHEN Y H, LI J F, WANG K, et al. Spark plasma sintering of Li/Ta-modified (K, Na)NbO3 lead-free piezoelectric ceramics: Post-annealing temperature effect on phase structure, electrical properties and grain growth behavior[J]. Mater Sci Eng B, 2011, 176(14): 1110–1114.

[99] [99] HOSHINA T. Size effect of Barium titanate: Fine particles and ceramics[J]. J Ceram Soc Japan, 2013, 121(1410): 156–161.

[100] [100] BUESSEM W R, CROSS L E, GOSWAMI A K. Phenomenological theory of high permittivity in fine-grained Barium titanate[J]. J Am Ceram Soc, 1966, 49(1): 33–36.

[101] [101] CURECHERIU L, BUSCAGLIA M T, BUSCAGLIA V, et al. Grain size effect on the nonlinear dielectric properties of Barium titanate ceramics[J]. Appl Phys Lett, 2010, 97(24): 242909.

[102] [102] TAN Y Q, ZHANG J L, WANG C L, et al. Enhancement of electric field-induced strain in BaTiO3 ceramics through grain size optimization[J]. Phys Status Solidi A, 2015, 212(2): 433–438.

[104] [104] HUAN Y, WANG X H, FANG J, et al. Grain size effect on piezoelectric and ferroelectric properties of BaTiO3 ceramics[J]. J Eur Ceram Soc, 2014, 34(5): 1445–1448.

[105] [105] WANG X H, DENG X Y, WEN H, et al. Phase transition and high dielectric constant of bulk dense nanograin Barium titanate ceramics[J]. Appl Phys Lett, 2006, 89(16): 162902.

[106] [106] TAKAHASHI H, NUMAMOTO Y, TANI J J, et al. Lead-free Barium titanate ceramics with large piezoelectric constant fabricated by microwave sintering[J]. Jpn J Appl Phys, 2006, 45(1L): L30.

[107] [107] SHAO S F, ZHANG J L, ZHANG Z, et al. High piezoelectric properties and domain configuration in BaTiO3 ceramics obtained through the solid-state reaction route[J]. J Phys D: Appl Phys, 2008, 41(12): 125408.

[108] [108] GHOSH D, SAKATA A, CARTER J, et al. Ferroelectric materials: Domain wall displacement is the origin of superior permittivity and piezoelectricity in BaTiO3 at intermediate grain sizes[J]. Adv Funct Mater, 2014, 24(7): 884.

[109] [109] HOSHINA T, TAKIZAWA K, LI J Y, et al. Domain size effect on dielectric properties of Barium titanate ceramics[J]. Jpn J Appl Phys, 2008, 47(9S): 7607.

[110] [110] GHOSH D, SAKATA A, CARTER J, et al. Domain wall displacement is the origin of superior permittivity and piezoelectricity in BaTiO3 at intermediate grain sizes[J]. Adv Funct Mater, 2014, 24(7): 885–896.

[111] [111] TAN Y Q, ZHANG J L, WU Y Q, et al. Unfolding grain size effects in Barium titanate ferroelectric ceramics[J]. Sci Rep, 2015, 5: 9953.

[112] [112] DAI B W, ZHENG P, BAI W F, et al. Direct and converse piezoelectric grain-size effects in BaTiO3 ceramics with different Ba/Ti ratios[J]. J Eur Ceram Soc, 2018, 38(12): 4212–4219.

[113] [113] MARTIRENA H T, BURFOOT J C. Grain-size effects on properties of some ferroelectric ceramics[J]. J Phys C Solid State Phys, 1974, 7(17): 3182–3192.

[114] [114] WESTON T B, WEBSTER A H, MCNAMARA V M. Lead zirconate-lead titanate piezoelectric ceramics with iron oxide additions[J]. J Am Ceram Soc, 1969, 52(5): 253–257.

[115] [115] OKAZAKI K, NAGATA K. Effects of grain size and porosity on electrical and optical properties of PLZT ceramics[J]. J Am Ceram Soc, 1973, 56(2): 82–86.

[116] [116] KIM S, LEE G S, SHROUT T R, et al. Fabrication of fine-grain piezoelectric ceramics using reactive calcination[J]. J Mater Sci, 1991, 26(16): 4411–4415.

[117] [117] ZHANG Z W, RAJ R. Influence of grain size on ferroelastic toughening and piezoelectric behavior of lead zirconate titanate[J]. J Am Ceram Soc, 1995, 78(12): 3363–3368.

[118] [118] OKAZAKI K, SAKATA K. Space charge polarization and aging of barium titanate ceramics[J]. Electro J Jpn, 1962, 7: 13–18.

[119] [119] LIU W, XU J, LV R F, et al. Effects of sintering behavior on piezoelectric properties of porous PZT ceramics[J]. Ceram Int, 2014, 40(1): 2005–2010.

[120] [120] GENENKO Y A, GLAUM J, HOFFMANN M J, et al. Mechanisms of aging and fatigue in ferroelectrics[J]. Mater Sci Eng B, 2015, 192: 52–82.

[121] [121] EITEL R E, SHROUT T R, RANDALL C A. Nonlinear contributions to the dielectric permittivity and converse piezoelectric coefficient in piezoelectric ceramics[J]. J Appl Phys, 2006, 99(12): 124110–124117.

[122] [122] HOFFMANN M J, HAMMER M, ENDRISS A, et al. Correlation between microstructure, strain behavior, and acoustic emission of soft PZT ceramics[J]. Acta Mater, 2001, 49(7): 1301–1310.

[123] [123] SCHULTHEI J, CHECCHIA S, URI H, et al. Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics[J]. J Eur Ceram Soc, 2020, 40(12): 3965–3973.

[124] [124] BELL A J, MOULSON A J, CROSS L E. The effect of grain size on the permittivity of BaTiO3[J]. Ferroelectrics, 1984, 54(1): 147–150.

[125] [125] ZHUKOV S, KUNGL H, GENENKO Y A, et al. Statistical electric field and switching time distributions in PZT 1Nb2Sr ceramics: Crystal- and microstructure effects[J]. J Appl Phys, 2014, 115(1): 014103.

[126] [126] DAMJANOVIC D, DEMARTIN M, SHULMAN H S, et al. Instabilities in the piezoelectric properties of ferroelectric ceramics[J]. Sens Actuat A Phys, 1996, 53(1–3): 353–360.

[127] [127] HRDTL K H, RAU H. PbO vapour pressure in the Pb(Ti1–x)O3 system[J]. Solid State Commun, 1969, 7(1): 41–45.

[128] [128] CHO C R, GRISHIN A. Background oxygen effects on pulsed laser deposited Na0.5K0.5NbO3 films: From superparaelectric state to ferroelectricity[J]. J Appl Phys, 2000, 87(9): 4439–4448.

[129] [129] ZHENG T, WU J G, XIAO D Q, et al. Recent development in lead-free perovskite piezoelectric bulk materials[J]. Prog Mater Sci, 2018, 98: 552–624.

[130] [130] ZHANG M H, LIU Y X, WANG K, et al. Origin of high electromechanical properties in (K, Na)NbO3-based lead-free piezoelectrics modified with BaZrO3[J]. Phys Rev Mater, 2020, 4(6): 064407.

[131] [131] ERIKSSON M, YAN H X, VIOLA G, et al. Ferroelectric domain structures and electrical properties of fine-grained lead-free sodium potassium niobate ceramics[J]. J Am Ceram Soc, 2011, 94(10): 3391–3396.

[132] [132] FENG Y, WU J G, CHI Q G, et al. Defects and aliovalent doping engineering in electroceramics[J]. Chem Rev, 2020, 120(3): 1710–1787.

[133] [133] ZHAO Z H, DAI Y J, HUANG F. The formation and effect of defect dipoles in lead-free piezoelectric ceramics: A review[J]. Sustain Mater Technol, 2019, 20: e00092.

[134] [134] CEN Z Y, FENG M Y, CAO F Z, et al. Improving high-field strain and temperature stability on KNN-based ceramics sintered in reducing atmosphere via defect engineering[J]. J Materiomics, 2024, 10(6): 1165–1175.

[135] [135] ZHANG L L, WANG X S, YANG W, et al. Structure and relaxor behavior of BaTiO3–CaTiO3–SrTiO3 ternary system ceramics[J]. J Appl Phys, 2008, 104(1): 014104.

[136] [136] WANG X S, YAMADA H, XU C N. Large electrostriction near the solubility limit in BaTiO3–CaTiO3 ceramics[J]. Appl Phys Lett, 2005, 86(2): 014104.

[137] [137] ZHU L F, ZHANG B P, ZHAO L, et al. High piezoelectricity of BaTiO3–CaTiO3–BaSnO3 lead-free ceramics[J]. J Mater Chem C, 2014, 2(24): 4764–4771.

[138] [138] MCZKA M, SIERADZKI A, BONDZIOR B, et al. Effect of aliovalent doping on the properties of perovskite-like multiferroic formates[J]. J Mater Chem C, 2015, 3(36): 9337–9345.

[139] [139] CASILLAS-TRUJILLO L, ANDERSSON D A, DORADO B, et al. Intrinsic defects, nonstoichiometry, and aliovalent doping of ABO perovskite scintillators[J]. Phys Status Solidi B: , 2014, 251(11): 2279–2286.

[140] [140] MOROZOV M I, DAMJANOVIC D. Hardening-softening transition in Fe-doped Pb(Zr, Ti)O3 ceramics and evolution of the third harmonic of the polarization response[J]. J Appl Phys, 2008, 104(3): 034107.

[141] [141] PARK H Y, SEO I T, CHOI M K, et al. Microstructure and piezoelectric properties of the CuO-added (Na0.5K0.5)(Nb0.97Sb0.03)O3 lead-free piezoelectric ceramics[J]. J Appl Phys, 2008, 104(3): 034103.

[142] [142] YANG S L, TSAI C C, HONG C S, et al. Effects of sintering aid CuTa2O6 on piezoelectric and dielectric properties of sodium potassium niobate ceramics[J]. Mater Res Bull, 2012, 47(4): 998–1003.

[143] [143] LIU Y X, QU W B, THONG H C, et al. Isolated-oxygen-vacancy hardening in lead-free piezoelectrics[J]. Adv Mater, 2022, 34(29): e2202558.

[144] [144] XU Z, LIU Y X, AZADEH M, et al. Identifying the interfacial polarization in non-stoichiometric lead-free perovskites by defect engineering[J]. Angew Chem Int Ed Engl, 2023, 62(9): e202216776.

[145] [145] SUN E W, CAO W W. Relaxor-based ferroelectric single crystals: Growth, domain engineering, characterization and applications[J]. Prog Mater Sci, 2014, 65: 124–210.

[146] [146] ZHANG S J, LI F. High performance ferroelectric relaxor-PbTiO3 single crystals: Status and perspective[J]. J Appl Phys, 2012, 111(3): 52968948.

[147] [147] KOU Q W, YANG B, SUN Y, et al. Tetragonal (Ba, Ca) (Zr, Ti)O3 textured ceramics with enhanced piezoelectric response and superior temperature stability[J]. J Materiomics, 2022, 8(2): 366–374.

[148] [148] MESSING G L, TROLIER-MCKINSTRY S, SABOLSKY E M, et al. Templated grain growth of textured piezoelectric ceramics[J]. Crit Rev Solid State Mater Sci, 2004, 29(2): 45–96.

[149] [149] MESSING G L, POTERALA S, CHANG Y F, et al. Texture-engineered ceramics—Property enhancements through crystallographic tailoring[J]. J Mater Res, 2017, 32(17): 3219–3241.

[150] [150] CHANG Y F, WU J, LIU Z, et al. Grain-oriented ferroelectric ceramics with single-crystal-like piezoelectric properties and low texture temperature[J]. ACS Appl Mater Interfaces, 2020, 12(34): 38415–38424.

[151] [151] YANG S, LI J L, LIU Y, et al. Textured ferroelectric ceramics with high electromechanical coupling factors over a broad temperature range[J]. Nat Commun, 2021, 12(1): 1414.

[152] [152] WU J, ZHANG S J, LI F. Prospect of texture engineered ferroelectric ceramics[J]. Appl Phys Lett, 2022, 121(12): 120501.

[153] [153] DHARMENDRA C, RAO K P, PRASAD Y V R K, et al. Hot working mechanisms and texture development in Mg-3Sn-2Ca-0.4Al alloy[J]. Mater Chem Phys, 2012, 136(2/3): 1081–1091.

[154] [154] SEMIATIN S L, BIELER T R. Effect of texture and slip mode on the anisotropy of plastic flow and flow softening during hot working of Ti-6Al-4V[J]. Metall Mater Trans A, 2001, 32(7): 1787–1799.

[155] [155] LIU Y C, ZHANG H J, SHI W M, et al. Ultra-low strain hysteresis in BaTiO3-based piezoelectric multilayer actuators via microstructural texture engineering[J]. J Materiomics, 2025, 11(2): 100882.

[156] [156] MOURE A. Review and perspectives of aurivillius structures as a lead-free piezoelectric system[J]. Appl Sci, 2018, 8(1): 62.

[157] [157] LI Z, QI W Z, CAO J, et al. Spark plasma sintering of grain-oriented Sr2Bi4Ti5O18 aurivillius phase ceramics[J]. J Alloys Compd, 2019, 782: 6–9.

[158] [158] HAERTLING G H, LAND C E. Hot-pressed (Pb, La)(Zr, Ti)O3 ferroelectric ceramics for electrooptic applications[J]. J Am Ceram Soc, 1971, 54(1): 1–11.

[159] [159] PARK S E, SHROUT T R. Ultrahigh strain and piezoelectric behavior in relaxor based ferroelectric single crystals[J]. J Appl Phys, 1997, 82(4): 1804–1811.

[160] [160] PARK S E, SHROUT T R. Characteristics of relaxor-based piezoelectric single crystals for ultrasonic transducers[J]. IEEE Trans Ultrason Ferroelectr Freq Contr, 1997, 44(5): 1140–1147.

[161] [161] MILISAVLJEVIC I, ZHANG M, JIANG Q H, et al. Transparent Electro-Optic Ceramics: Processing, materials, and applications[J]. J Materiomics, 2025, 11(2): 100872.

[162] [162] CHOI J J, RYU J, KIM H E. Microstructural evolution of transparent PLZT ceramics sintered in air and oxygen atmospheres[J]. J Am Ceram Soc, 2001, 84(7): 1465–1469.

[163] [163] HAERTLING G H. Improved hot-pressed electrooptic ceramics in the (Pb, La)(Zr, Ti)O3 system[J]. J Am Ceram Soc, 1971, 54(6): 303–309.

[164] [164] CHENG H J, HE X Y, ZENG X, et al. A novel vacuum/oxygen hot press sintering approach for the fabrication of transparent PLZT (7.4/70/30) ceramics[J]. Ceram Int, 2021, 47(7): 9620–9626.

[165] [165] ZU D, ZHANG Y X, LI H R, et al. Sintering pressure of SPS-inducing lattice deformation enhances ferroelectric and photoluminescence properties of PLZT ceramics[J]. J Mater Res, 2023, 38(11): 2894–2907.

[166] [166] YAN K, CHEN X L, WANG F F, et al. Large piezoelectricity and high transparency in fine-grained BaTiO3 ceramics[J]. Appl Phys Lett, 2020, 116(8): 082902.

[167] [167] SMITH W A. The role of piezocomposites in ultrasonic transducers[C]//Proceedings., IEEE Ultrasonics Symposium. Montreal, QC, Canada. IEEE, 1989: 755–766.

[168] [168] HIRATA Y, NUMAZAWA T, TAKADA H. Effects of aspect ratio of lead zirconate titanate on 1-3 piezoelectric composite properties[J]. Jpn J Appl Phys, 1997, 36(9S): 6062.

[169] [169] GURURAJA T R, SCHULZE W A, CROSS L E, et al. Piezoelectric composite materials for ultrasonic transducer applications. part II: Evaluation of ultrasonic medical applications[J]. IEEE Trans Sonics Ultrason, 1985, 32(4): 499–513.

[170] [170] JANAS V F, SAFARI A. Overview of fine-scale piezoelectric ceramic/polymer composite processing[J]. J Am Ceram Soc, 1995, 78(11): 2945–2955.

[171] [171] LUBITZ K, WOLFF A, PREU G, et al. PcI2: New piezoelectric composites for ultrasonic transducers[J]. Ferroelectrics, 1992, 133(1): 21–26.

[172] [172] LEE S H, MAEDA R, ESASHI M. Microfabrication of thick and bulk PZT materials for piezoelectric actuator[C]//SPIE Proceedings, Nano- and Microtechnology: Materials, Processes, Packaging, and Systems. Melbourne, Australia. SPIE, 2002.

[173] [173] WANG S N, LI J F, WATANABE R, et al. Fabrication of lead zirconate titanate microrods for 1–3 piezocomposites using hot isostatic pressing with silicon molds[J]. J Am Ceram Soc, 1999, 82(1): 213–215.