Dielectric and Piezoelectric Properties of KNbO3–NaNbO3–LiNbO3–SrTiO3 Ceramics

For the purpose of the developing Pb-free piezoelectric ceramics, the dielectric and piezoelectric properties of two series of KNbO 3 –NaNbO 3 –LiNbO 3 –SrTiO 3 (KN–NN–LN–ST) perovskite ceramics, namely 0.47KN–0.47NN–(0.06- x )LN– x ST (0≤ x ≤0.06) and 0.45KN–0.45NN–(0.10- y )LN– y ST (0.02≤ y ≤0.10) were investigated as functions of composition. In both series, the orthorhombic perovskite phase formed at lower temperatures, and was transformed to tetragonal form and then cubic form with increasing temperature. The orthorhombic–tetragonal transition temperature ( T ot ) and tetragonal–cubic transition temperature (Curie temperature, T c ) gradually shifted toward lower temperatures with increasing ST content. For the 0.47KN–0.47NN–(0.06- x )LN– x ST series, the T ot =100 °C and T c =500 °C for x =0, and the T ot =-20 °C and T c =220 °C for x =0.06. For the 0.45KN–0.45NN–(0.10- y )LN– y ST series, T ot =-30 °C and T c =450 °C for y =0.02, and T ot =-60 °C and T c =330 °C for y =0.05. Among the ceramics obtained, the 0.45KN–0.45NN–0.06LN–0.04ST composition showed relatively good piezoelectric properties, k p =0.33 and d 33 =120 pC/N, which are comparable to those of Pb-free piezoelectric ceramics previously reported.