Crystalline structural phase boundaries in (K,Na,Li)NbO3 ceramics

Lead-free (KxNa1-x)(1-y)LiyNbO3 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 inicrostructures, 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 (K0.50Na0.50)(1-y)LiyNbO3 ceramics at y = 0.05-0.06, which corresponds to the previously reported morphotropic phase boundary (MPB). The other two appear in (KxNa1-x)(0.94)Li0.06NbO3 ceramics near x = 0.40 and x = 0.60, respectively. (K0.50Na0.50)(0.935)Li0.065NbO3 and (K0.45Na0.55)(0.94)Li0.06NbO3 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. (C) 2008 Elsevier Ltd. All rights reserved.