Giant high-temperature electrostrain in BiFeO₃-BaTiO₃ ceramics via SrZrO₃-induced morphotropic phase boundary and defect-mediated domain engineering

The 0.60BiFeO₃−0.40BaTiO₃-SrZrO₃ (BF40BT-xSZ) compositional system is engineered to establish a morphotropic phase boundary (MPB) between coexisting tetragonal and pseudocubic phases (T+PC). Our results demonstrate that progressive incorporation of SZ not only enhances relaxor characteristics but also significantly suppresses leakage currents (from 3.8 × 10⁻⁷ to 5.9 × 10⁻⁸ A/cm²). Further studies reveal that the improved insulation originates from the inhibition of Fe³⁺→Fe²⁺ reduction, thereby reducing oxygen vacancy (V O · ·) concentrations and optimizing ferroelectric domain dynamics. Consequently, a high remnant polarization (P_m) of 34.18 μC/cm² and a substantial unipolar strain (S _max^Uni) of 0.302% at room temperature are achieved, with S _max^Uni further escalating to a record-breaking 0.85% at 120 °C. This exceptional high-temperature performance is ascribed to the unpinning and mobility enhancement of domain walls and the coexistence of nanodomains and polar nanoregions, which facilitate spontaneous polarization rotation and collectively enhance strain response. These findings establish the BF40BT-xSZ system as a compelling candidate for high-temperature piezoelectric actuators.