Hydrothermal-assisted synthesis and sintering of K0.5Na0.5NbO3−xLiTaO3 lead-free piezoelectric ceramics

Pure KNbO3, NaNbO3 and LiTaO3 powers were synthesized by the hydrothermal method at low reaction temperature and K0.5Na0.5NbO3–xLiTaO3 (KNN–xLT) lead-free piezoelectric ceramics were fabricated by normal sintering. The paper mainly focused on the relationship among the microstructure, the phase transition, and the electrical properties of KNN–xLT ceramics synthesized by the hydrothermal assisted method. The polymorphic phase boundary (PPB) between orthorhombic and tetragonal phases appears around x=6 mol% LT at room temperature. The piezoelectric and the electromechanical properties are enhanced for the composition near the polymorphic phase boundary. The piezoelectric constant values (d33) reach to 187 pC/N, the electromechanical coupling coefficients (kp) of planar mode reach to 37%, the Curie temperature (Tc) and remanent polarization (Pr) reach to 461.8 °C and 19.85 μC/cm, respectively. The results show that KNN–LT is a kind of good lead-free piezoelectric ceramic.