Domain Engineering of Lead‐Free Li‐Modified (K,Na)NbO3 Polycrystals with Highly Enhanced Piezoelectricity

Abstract Aging and re‐poling induced enhancement of piezoelectricity are found in (K,Na)NbO 3 (KNN)‐based lead‐free piezoelectric ceramics. For a compositionally optimized Li‐doped composition, its piezoelectric coefficient d 33 can be increased up to 324 pC N −1 even from a considerably high value (190 pC N −1 ) by means of a re‐poling treatment after room‐temperature aging. Such a high d 33 value is only reachable in KNN ceramics with complicated modifications using Ta and Sb dopants. High‐angle X‐ray diffraction analysis reveals apparent changes in the crystallographic orientations related to a 90° domain switching before and after the aging and re‐poling process. A possible mechanism considering both defect migration and rotation of spontaneous polarization explains the experimental results. The present study provides a general approach towards piezoelectric response enhancement in KNN‐based piezoelectric ceramics.