Microstructure and piezoelectric properties of 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 ceramics

For 0.95(Na0.5K0.5)NbO3–0.05BaTiO3 (0.95NKN-0.05BT) ceramics sintered at 1040–1075°C, abnormal grain growth occurred but the grain size decreased when the sintering temperature exceeded 1075°C. The dielectric constant (ϵ3T∕ϵ3), electromechanical coupling factor (kp), and piezoelectric constant (d33) were considerably increased with increasing relative density and grain size. Evaporation of Na2O deteriorated the piezoelectric properties by decreasing the resistivity. To minimize Na2O evaporation, specimens were muffled with 0.95NKN-0.05BT powders during the sintering. Improved piezoelectric properties of d33=225pC∕N, kp=36%, and ϵ3T∕ϵ3=1058 were obtained for specimen sintered at 1060°C for 2h with muffling.