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

Aging and re-poling induced enhancement of piezoelectricity are found in (K,Na)NbO3 (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 degrees 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.