Influence of sintering conditions on piezoelectric properties of KNbO3 ceramics

A homogeneous KNbO3 (KN) phase was formed in specimens that were sintered at 1020 °C and 1040 °C, without formation of the K2O-deficient secondary phase, indicating that the amount of evaporation of K2O during sintering was very small. However, the KN liquid phase was formed during sintering and assisted the densification of the KN ceramics. A dense microstructure was developed in the specimen sintered at 1020 °C for 6 h and abnormal grain growth occurred in this specimen. A similar microstructure was observed in the specimens sintered at 1040 °C for 1.0 h. The dielectric and piezoelectric properties of the KN ceramics were considerably influenced by the relative density. The KN ceramics sintered at 1020 °C for 6 h, which showed a large relative density that was 95% of the theoretical density, exhibited promising electrical properties: ɛT33/ɛo of 540, d33 of 109 pC/N, kp of 0.29, and Qm of 197.