Piezoelectric properties in perovskite 0.948(K_0.5Na _0.5)NbO₃-0.052LiSbO₃ lead-free ceramics

Lead-free piezoelectric ceramics, with the nominal composition of 0.948 (K0.5 Na0.5) Nb O3 -0.052LiSb O3 (KNN-LS5.2), were synthesized by conventional solid-state sintering, and the piezoelectric and electromechanical properties were characterized as a function of temperature. The Curie temperature of the KNN based perovskite material was found to be 368 °C with an orthorhombic-tetragonal polymorphic phase transition (TO-T) temperature at approximately ∼35 °C. The room temperature dielectric permittivity (ε33T ε0) and loss were found to be 1380 and 2%, respectively, with piezoelectric properties of k33 ∼62% and d33 ∼265 pCN and k31 ∼30% and d31 ∼-116 pCN. The temperature dependence of the properties mimicked the compositional variation seen in the proximity of a morphotropic phase boundary [e.g., lead zirconate titanate (PZT)], with a maxima in the dielectric and piezoelectric properties and a corresponding "softening" of the elastic properties. Unlike that found for PZT-type materials, the modified KNN material exhibited characteristics of both "soft" and "hard" piezoelectricities owing to the distinctly different domain states associated with orthorhombic and tetragonal phases.