Deciphering the thermal depolarization mechanism to enhance the temperature stability of bismuth layer-structured piezoceramics

Bismuth layer-structured piezoceramics (BLSPs) hold great potential for structural health monitoring in aerospace engines and nuclear reactors, yet their thermal depolarization mechanisms remain unclear, severely limiting the development of materials with excellent temperature stability. Here, through ingeniously designed heat treatment experiments and multiscale structural characterization, we reveal that the random migration of oxygen vacancies at high temperatures leads to the disruption of interfacial polarization, while uncontrollable merging of micro-domains also occurs, and both factors jointly affect the temperature stability of the material. Building upon this physical understanding, we propose a general strategy to improve the temperature stability of BLSPs by constructing defect dipoles to regulate the migration kinetics of oxygen vacancies and to pin domain walls. Utilizing this strategy, outstanding temperature stability (piezoelectric coefficient d 33 variation