Low temperature sintering and piezoelectric properties of lead-free (1-x) (Na0.5K0.5)NbO3-xCaTiO3 ceramics

The 0.95NKN-0.05CaTiO3 (0.95NKN-0.05CT) ceramics showed the high piezoelectric properties of d33=241, kp=0.41 and e3T/eo=1316. Therefore, the 0.95NKN-0.05CT ceramic is considered to be a promising candidate for lead-free piezoelectric material. However, its sintering temperature was high and Na2O evaporation occurred. Moreover, Na2O evaporation decreased the specimen resistivity and thus the poling efficiency. Therefore, the sintering temperature of this material needs to be decreased before it gains practical application. Moreover, the decreased sintering temperature is required to allow its application to multilayer devices. In this work, CuO was used to lower the sintering temperature of the 0.95NKN-0.05CT ceramics and variations of microstructure and piezoelectric properties of 0.95NKN-0.05CT ceramics were investigated with CuO addition. The piezoelectric properties of the specimens were considerably influenced by the relative density, grain size and liquid phase amount. The high piezoelectric properties of d33 = 200 pC/N, kp = 0.37, e3T/eo = 1173 and Qm = 350 were obtained for the 0.95NKN-0.05CT ceramics containing 2.0 mol% CuO sintered at 960 oC for 10 h.