Structural and piezoelectric properties of MnO2-added 0.95(Na0.5K0.5)NbO3–0.05SrTiO3 ceramics

The structural and piezoelectric properties of the x mol% MnO2-added 0.95(Na0.5−x/200K0.5−x/200)NbO3–0.05SrTiO3 [(NK)xMN-ST] ceramics were investigated. A dense microstructure with enlarged grains was formed for the specimens sintered at 1040 °C through liquid-phase sintering. However, the grain size decreased for the specimen sintered at 1060 °C because of the formation of a large amount of the liquid phase. Therefore, the microstructural variations in the (NK)xMN-ST ceramics can be explained by liquid-phase-assisted abnormal grain growth. The specimens sintered at 1020 and 1060 °C showed low piezoelectric properties because of their low relative density and small grain size, respectively. On the other hand, the (NK)xMN-ST ceramic with x = 0.1 sintered at 1040 °C showed promising piezoelectric properties: d33 = 260 pC/N, kp = 0.42, Qm = 202 and ε33T/ε0=1291.