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.