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

Lead-free (KxNa1−x)1−yLiyNbO3 ceramics (with x=0.50x=0.50, y=0–0.08y=0–0.08 and x=0.30–0.70x=0.30–0.70, y=0.06y=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 (K0.50Na0.50)1−yLiyNbO3 ceramics at y=0.05–0.06y=0.05–0.06, which corresponds to the previously reported morphotropic phase boundary (MPB). The other two appear in (KxNa1−x)0.94Li0.06NbO3 ceramics near x=0.40x=0.40 and x=0.60x=0.60, respectively. (K0.50Na0.50)0.935Li0.065NbO3 and (K0.45Na0.55)0.94Li0.06NbO3 ceramics show high piezoelectric properties with the d33d33 values over 200 pC/N and the kpkp 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.