Exploring the mechanisms of enhanced piezoelectric properties in (K,Na)NbO3 single crystals

(K,Na)NbO 3 (KNN)-based piezoelectric materials are candidates for replacing Pb-based materials. However, the piezoelectric properties of existing KNN-based single crystals are still inferior to those of Pb-based relaxor ferroelectric single crystals. Moreover, the piezoelectric response mechanism of KNN-based single crystals remains unclear. In this study, (Li,K,Na)(Nb,Sb,Ta)O 3 :Mn (KNNLST:Mn) single crystals with an excellent piezoelectric coefficient d 33 of approximately 778 pC/N were prepared. Systematically studies of intrinsic and extrinsic piezoelectric responses have revealed that the high d 33 of KNNLST:Mn single crystals is related to the shear piezoelectric response of a single-domain state and irreversible domain wall motion of the engineering domains. Furthermore, the effect of the orthorhombic (O)-tetragonal (T) phase boundary on intrinsic and extrinsic piezoelectric response is systematically studied, and the impact mechanism is elucidated. The results indicate that a lower dielectric response and elastic constant limit the intrinsic shear piezoelectric response of KNNLST:Mn single crystals, and approaching the O–T phase boundary can enhance both intrinsic and extrinsic piezoelectric responses. This study improves our understanding of the structure-performance relationship in KNN-based single crystals and offers insights for optimizing piezoelectric properties in KNN-based materials. • Construction of room temperature polymorphic phase transitions. • KNNLST:Mn single crystals with a "4O" structure achieved a d 33 value of 778 pC/N. • The origin of the high piezoelectric properties of KNNLST:Mn single crystals revealed from both intrinsic and extrinsic aspects.