[1] AKSEL E, JONES J L. Advances in lead-free piezoelectric materials for sensors and actuators[J]. Sensors, 1935(2010).

[2] RODEL J, WEBBER K G, DITTMER R et al. Transferring lead-free piezoelectric ceramics into application[J]. J. Eur. Ceram. Soc., 1659(2015).

[3] DAMJANOVIC D. Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics[J]. Rep. Prog. Physics, 1267(1998).

[4] RODEL J, LI F. Lead-free piezoceramics: status and perspectives[J]. MRS Bull., 576(2018).

[5] PISARENKO G, KOVALEV S P, CHUSHKO V M. Fracture toughness of piezoelectric ceramics[J]. Strength Mater., 1492(1980).

[6] RODIG T, SCHONECKER A, GERLACH G. A survey on piezoelectric ceramics for generator applications[J]. J. Am. Ceram. Soc., 901(2010).

[7] GALLEGO-JUAREZ J A. Piezoelectric ceramics and ultrasonic transducers[J]. J. Phys. E Sci. Instrum., 804(1989).

[8] PFERNER R A, THURN G, ALDINGER F. Mechanical properties of PZT ceramics with tailored microstructure[J]. Mater. Chem. Phys., 24(1999).

[9] LI F X, FANG D N, SOH A K. Theoretical saturated domain- orientation states in ferroelectric ceramics[J]. Scr. Mater., 1241(2006).

[10] CALDERON-MORENO J M, POPA M. Fracture Toughness Anisotropy by Indentation and SEVNB on Tetragonal PZT Polycrystals[conf-proc](2001).

[11] LI Y W, LI F X. Large anisotropy of fracture toughness in mechanically poled/depoled ferroelectric ceramics[J]. Scr. Mater., 313(2010).

[12] CALDERON-MORENO J M, GUIU F, MEREDITH M et al. Fracture toughness anisotropy of PZT[J]. Mater. Sci. Eng. A, 1062(1997).

[13] MEHTA K, VIRKAR A V. Fracture mechanisms in ferroelectric- ferroelastic lead zirconate titanate (Zr: Ti=0.54:0.46) ceramics[J]. J. Am. Ceram. Soc., 567(1990).

[14] LUCATO SLDE, LUPASCU DC, RODEL J. Effect of poling direction on R-curve behavior in lead zirconate titanate[J]. J. Am. Ceram. Soc., 424(2000).

[15] FETT T, GLAZOUNOV A, HOFFMANN M J et al. On the interpretation of different R-curves for soft PZT[J]. Eng. Fract. Mech., 1207(2001).

[16] SEO Y H, VOGLER M, ISAIA D et al. Temperature-dependent R-curve behavior of Pb(Zr_1-xTi_x)O₃[J]. Acta Mater., 6418(2013).

[17] SCHNEIDER G A. Influence of electric field and mechanical stresses on the fracture of ferroelectrics[J]. Annu. Rev. Mater. Res., 491(2007).

[18] LI Y W, LIU Y, OCHSNER P E et al. Temperature dependent fracture toughness of KNN-based lead-free piezoelectric ceramics[J]. Acta Mater., 369(2019).

[19] KUNA M. Fracture mechanics of piezoelectric materials-where are we right now?[J]. Eng. Fract. Mech., 309(2010).

[20] WEBBER K G, VOGLER M, KHANSUR N H et al. Review of the mechanical and fracture behavior of perovskite lead-free ferroelectrics for actuator applications[J]. Smart Mater. Struct., 063001(2017).

[21] KIM S B, KIM D Y, KIM J J et al. Effect of grain size and poling on the fracture mode of lead zirconate titanate ceramics[J]. J. Am. Ceram. Soc., 161(1990).

[22] GUILLON O, THIEBAUD F, PERREUX D et al. New considerations about the fracture mode of PZT ceramics[J]. J. Am. Eur. Soc., 2421(2005).

[23] KUBLER J. Fracture toughness of ceramics using the SEVNB method a joint VAMSA/ESIS round robin[J]. Fract. Mech. Ceram., 437(2002).

[24] SALEM J A. Fracture toughness of advanced ceramics at room temperature[J]. J. Res. Natl. Inst. Stand. Technol., 579(1992).

[25] VOGLER M, FETT T, RODEL J. Crack-tip toughness of lead-free (1-x)(Na_1/2Bi_1/2)TiO₃-xBaTiO₃ piezoceramics[J]. J. Am. Ceram. Soc., 5304(2018).

[26] LI F X, SOH A K. An optimization-based computational model for domain evolution in polycrystalline ferroelastics[J]. Acta Mater., 2207(2010).

[27] BERMEJO R, DELUCA M. Mechanical characterization of PZT ceramics for multilayer piezoelectric actuators[J]. J. Ceram. Sci. Technol., 159(2012).

[28] BERMEJO R, GRUNBICHLER H, KREITH J et al. Fracture resistance of a doped PZT ceramic for multilayer piezoelectric actuators: Effect of mechanical load and temperature[J]. J. Eur. Ceram. Soc., 705(2010).

[29] JELITTO H, KEBLER H, SCHNEIDER G A et al. Fracture behavior of poled piezoelectric PZT under mechanical and electrical loads[J]. J. Eur. Ceram. Soc., 749(2005).

[30] DENKHAUS S M, VOGLER M, NOVK N et al. Short crack fracture toughness in (1-x)(Na^1/2Bi^1/2)TiO₃-xBaTiO₃ relaxor ferroelectrics[J]. J. Am. Ceram. Soc., 4760(2017).