Phase coexistence and high piezoelectric properties in (K_0.40Na_0.60)_0.96Li_0.04Nb_0.80Ta_0.20O₃ceramics

Abstract

Lead-free (KxNa1−x)0.96Li0.04 Nb0.80Ta0.20O3 ceramics with x = 0.10–0.70 were prepared by the conventional solid-state reaction technique. The influence of the K/Na ratio on the microstructure, crystallographic structure, phase transition and piezoelectric properties was investigated. It has been disclosed that the phase transition temperature TO–T drastically decreases with x in the narrow compositional range of x = 0.30–0.40 and the phase coexistence of the orthorhombic structure and the tetragonal structure occurs near x = 0.40. The ceramics with x = 0.40 shows high piezoelectric properties (d33 = 254 pC N−1, kp = 51.5%, kt = 49.4% and k33 = 66.6%, respectively) with low dielectric loss (tan δ = 1.5%) and weak temperature dependence between 10 and 85 °C. In particular, the piezoelectric properties remain almost unchanged in the thermal ageing test from −125 to 300 °C. Therefore, this ceramic is considered to be a very promising lead-free piezoelectric material for practical applications. The relation of piezoelectric properties with morphotropic phase boundary and polymorphic phase transition was discussed.