Crystalline structural phase boundaries in (K,Na,Li)NbO 3 ceramics

Abstract

Lead-free (K x Na 1− x ) 1− y Li y NbO 3 ceramics (with x = 0.50 , y = 0 – 0.08 and x = 0.30 – 0.70 , y = 0.06 , respectively) were synthesized using the conventional solid-state reaction technique. Compositional influences of K, Na and Li constituents on microstructures, crystalline structures, dielectric and piezoelectric properties were investigated. It has been known that microstructures change largely with the alkali constituents and that there exist three orthorhombic-tetragonal phase boundaries at room temperature. One occurs in (K 0.50Na 0.50) 1− y Li y NbO 3 ceramics at y = 0.05 – 0.06 , which corresponds to the previously reported morphotropic phase boundary (MPB). The other two appear in (K x Na 1− x ) 0.94Li 0.06NbO 3 ceramics near x = 0.40 and x = 0.60 , respectively. (K 0.50Na 0.50) 0.935Li 0.065NbO 3 and (K 0.45Na 0.55) 0.94Li 0.06NbO 3 ceramics show high piezoelectric properties with the d 33 values over 200 pC/N and the k p values around 45% at room temperature. It is thought that the observed high piezoelectric properties are largely affected by the temperature-driven orthorhombic-tetragonal phase transition.