Piezoelectric properties in perovskite 0.948(K0.5Na0.5)NbO3-0.052LiSbO3 lead-free ceramics

Lead-free piezoelectric ceramics, with the nominal composition of 0.948(K_0.5Na_0.5)NbO₃-0.052LiSbO₃ (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 (T_O-T) temperature at approximately ∼35°C. The room temperature dielectric permittivity (ɛ₃₃^T/ɛ₀) and loss were found to be 1380 and 2%, respectively, with piezoelectric properties of k₃₃∼62% and d₃₃∼265pC /N and k₃₁∼30% and d₃₁∼-116pC/N. 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.