Defect dipole stretching enables ultrahigh electrostrain

Piezoelectric actuators have been extensively utilized as micro-displacement devices because of their advantages of large output displacement, high sensitivity, and immunity to electromagnetic interference. Here, we propose a straightforward approach to design <110>-oriented defect dipoles by introducing A-site vacancies and oxygen vacancies in (K_0.48Na_0.52)_0.99NbO_2.995 ceramics. As a result, we achieve ultrahigh electrostrains of 0.7% at 20 kV cm^-1 (with an effective piezoelectric strain coefficient d₃₃^* = 3500 pm V^-1), outperforming the performance of existing piezoelectric ceramics at the same driving field. The exceptional electrostrain is primarily attributed to the large stretching of defect dipoles when subjected to an applied electric field, a phenomenon that has been experimentally confirmed. Moreover, the strong interaction between these defect dipoles and <110> spontaneous polarizations plays a critical role in minimizing hysteresis and ensuring excellent fatigue resistance. Our findings present a practical and effective strategy for developing high-performance piezoelectric materials tailored for advanced actuator applications.