Intrinsic and extrinsic contributions induced by phase transition to piezoelectric response in KNN-based ceramics

As a kind of typical lead-free piezoelectric ceramics, potassium sodium niobate (K_0.5Na_0.5NbO₃, KNN)-based ceramics have attracted wide attention because of excellent piezoelectric performance and high Curie temperature. Although the performance has been significantly optimized by phase structure regulation, the original mechanism is poorly defined. In this work, the effect of phase structures on intrinsic and extrinsic contributions to piezoelectric response are explored via Rayleigh analysis with increasing T phase. With the phase transition from R–O to R–O–T, the extrinsic contribution increases because of promoted domain switching from lowed polarization anisotropy with energy barrier. The enlarged extrinsic contribution as well as lowered intrinsic ones is obtained near O–T phase transition temperature due to promoted domain evolution and increase activity of domain under thermal field. Based on the evolution of contribution, the optimized ferroelectric/piezoelectric performance is always achieved for R–O–T phase boundary with enhanced T phase, originated by the strengthened extrinsic contribution. This work further reveals the origin of high piezoelectric response with multiphase coexistence, facilitating the development of high-performance piezoelectric materials.