Low temperature sintering of ZnO and MnO2-added (Na0.5K0.5)NbO3 ceramics

ZnO was used to decrease the sintering temperature of 1.5 mol% MnO2-added (Na0.5K0.5)NbO3(MNKN) ceramics. When a small amount of ZnO (≥2.0 mol%) was added, a dense microstructure was observed for specimens sintered at 960 °C, with high relative density of 96.0% of the theoretical density. The liquid phase, which was considered to be an Nb2O5–MnO–ZnO related phase, was formed in the ZnO-added MNKN ceramics and abnormal grain growth occurred in its presence. Therefore, although a very small amount of ZnO might enter the matrix of the MNKN, most of the ZnO was used to form the liquid phase and assisted the densification of the specimens, indicating that the hardening effect of Zn2+ was insignificant. The 2.0 mol% ZnO-added MNKN (ZMNKN) ceramics sintered at 960 °C exhibited the high piezoelectric properties of kp = 37%, ε3T/ε0=297, d33 = 120 pC/N, and Qm = 200. In addition, the reaction between the Ag electrode and the ZMNKN ceramic sintered at 960 °C was negligible.