Ferroelectric‒to‒relaxor crossover in KNN‒based lead‒free piezoceramics

Abstract

This study investigated the phase transition behavior and electrical properties of (K0.5Na0.5)(Nb1-xZrx)O3 (KNN‒100xZ) and (K0.5Na0.5)NbO3–yBaZrO3 (KNN–100yBZ) lead–free piezoelectric ceramics. The phase transitions in crystal structures were compared in KNN ceramics between single Zr4+ doping and Ba2+Zr4+ co−doping. Piezoelectric properties such as the piezoelectric constant (d33) and electromechanical coupling factor (kp) are optimized for KNN‒6BZ ceramics and were clarified via the polymorphic phase transition from the orthorhombic to pseudocubic phase. The fitted degree of diffuseness (γ) for a phase transition from the modified Curie–Weiss law indicated that KNN ceramics as ferroelectrics are gradually transformed through BaZrO3 modification. Accordingly, the enhanced strain properties at y = 0.08 consist of coexisting ferroelectric domains and polar nanoregions that are supported by ferroelectric–to–relaxor crossover in KNN‒100BZ ceramics.