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Over the past two decades, (K0.5Na0.5)NbO3 (KNN)-based lead-free piezoelectric ceramics have made significant progress. However, attaining a high electrostrain with remarkable temperature stability and minimal hysteresis under low electric fields has remained a significant challenge. To address this long-standing issue, we have employed a collaborative approach that combines defect engineering, phase engineering, and relaxation engineering. The LKNNS-6BZH ceramic, when sintered at Tsint = 1170 ℃, demonstrates an impressive electrostrain with a d33∗ value of 0.276% and 1379 pm·V–1 under 20 kV·cm–1, which is comparable to or even surpasses that of other lead-free and Pb(Zr,Ti)O3 ceramics. Importantly, the electrostrain performance of this ceramic remains stable up to a temperature of 125 ℃, with the lowest hysteresis observed at 9.73% under 40 kV·cm–1. These excellent overall performances are attributed to the presence of defect dipoles involving VA′–VO∙∙ and BNb′–VO∙∙, the coexistence of R–O–T multiphase, and the tuning of the trade-off between long-range ordering and local heterogeneity. This work provides a lead-free alternative for piezoelectric actuators and a paradigm for designing piezoelectric materials with outstanding comprehensive performance under low electric fields.

BiFeO3–BaTiO3 (BF–BT) based piezoelectric ceramics are a kind of high-temperature lead-free piezoelectric ceramics with great development prospects due to their high Curie temperature (TC) and excellent electrical properties. However, large leakage current limits their performance improvement and practical applications. In this work, direct current (DC) test, alternating current (AC) impedance, and Hall tests were used to investigate conduction mechanisms of 0.75BiFeO3–0.25BaTiO3 ceramics over a wide temperature range. In the range of room temperature (RT)−150 ℃, ohmic conduction plays a predominant effect, and the main carriers are p-type holes with the activation energy (Ea) of 0.51 eV. When T > 200 ℃, the Ea value calculated from the AC impedance and Hall data is 1.03 eV with oxygen vacancies as a cause of high conductivity. The diffusion behavior of thermally activated oxygen vacancies is affected by crystal symmetry, oxygen vacancy concentration, and distribution, dominating internal conduction mechanism. Deciphering the conduction mechanisms over the three temperature ranges would pave the way for further improving the insulation and electrical properties of BiFeO3–BaTiO3 ceramics.