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 6h and abnormal grain growth occurred in this specimen. A similar microstructure was observed in the specimens sintered at 1040°C for 1.0h. The dielectric and piezoelectric properties of the KN ceramics were considerably influenced by the relative density. The KN ceramics sintered at 1020°C for 6h, which showed a large relative density that was 95% of the theoretical density, exhibited promising electrical properties: e{open}^T₃₃/e{open}_o of 540, d₃₃ of 109pC/N, k_p of 0.29, and Q_m of 197.