Defect dipole gradient design in (K,Na)NbO3-based piezoelectric ceramics enabling controllable ultrahigh bending deformation

Piezoelectric ceramic bending actuators play a pivotal role in various high-tech applications. As a new strategy for fabricating bending actuators, constructing defect dipole concentration gradient has emerged as an effective strategy for boosting electro-bending displacement, yet achieving reproducibility remains challenging due to the uncontrollable alkali volatilization. Herein we propose a new strategy to fabricate barium-doped (K,Na)NbO₃ piezoelectric bending actuators with controllable gradient distribution of highly stable <110>-oriented ($V_{\mathrm{K}/\text{Na}}^{{}^{\prime }}$$V_{\mathrm{K}/\text{Na}}^{{}^{\prime }}$ – $V_{\mathrm{O}}^{··}$$V_{\mathrm{O}}^{··}$) defect dipoles, achieving a centimeter-level displacement performance of 1.2 cm under ± 200 V sinusoidal AC excitations. Samples with defect gradient design but lower oxygen vacancy content exhibit larger bending displacement and excellent fatigue stability without leakage conduction, confirming that the defect dipole concentration gradient, rather than oxygen vacancy migration drives the large bending deformation. Experimental analysis combined with phase-field simulations uncovers that the delicate concentration design of <110>-oriented defect dipoles within orthorhombic stripe domains plays crucial roles in controllable and stable displacement output. We validate the feasibility of the bending actuators in piezoelectric haptic feedback and piezoelectric micro-pump applications, providing new insights into the design of piezoceramic actuators.