Asymmetric Electrostrain/Electrobending in Piezoelectric Ceramics: Role of Defect Dipoles or Oxygen Vacancies

Atomic-scale defects in piezoelectric ceramics significantly influence their macroscopic electric field-induced deformation responses, which are critical for developing advanced piezoelectric actuators. Although the recently revealed giant electrostrain and electrobending have been attributed to defect dipoles or oxygen vacancies, deciphering their precise atomic configurations and specific roles remains a great challenge. In this study, the microscopic defect configurations and mesoscopic domain switching behaviors of different piezoelectric ceramics with macroscopic asymmetric electrostrain/electrobending are visualized. We demonstrate that the long-range migration of oxygen vacancies alters surface domain switching and induces poling-independent electrobending deformation in BaTiO₃ ceramics, while the formation of defect dipoles can effectively suppress such electrobending and cause poling-dependent asymmetric electrostrain. Notably, we found that the defect dipoles with a continuous gradient distribution will undergo self-alignment in (K, Na)NbO₃-based ceramics, thereby elucidating the origin of poling-direction-independent electrobending in piezoelectric ceramics with volatile elements. These findings mark a milestone in understanding the mechanism underlying giant defect-mediated electro-deformation, settle widely debated controversy about electrobending, and open new avenues for the rational design of advanced piezoelectric ceramics.