Piezoelectric Properties of Sn-Doped (K,Na)NbO3 Ceramics

It was previously reported that Ca-doped (K,Na)NbO 3 + ZrO 2 could be cofired with nickel inner electrodes in a reducing atmosphere. In the present study, the piezoelectric properties of Sn-doped (K,Na)NbO 3 + ZrO 2 ceramics were investigated. We prepared Sn-doped (K,Na)NbO 3 + ZrO 2 ceramics and Ca-doped (K,Na)NbO 3 + ZrO 2 ceramics by doping with Sn 2+ and Ca 2+ under reducing calcination. The Curie temperature $T_{\text{c}}$ of the Sn-doped (K,Na)NbO 3 + ZrO 2 was 300 °C, which was the same as that of the Ca-doped (K,Na)NbO 3 + ZrO 2 . The tetragonal--orthorhombic phase transition temperature and piezoelectric constant $d_{33}$ of the Ca-doped (K,Na)NbO 3 + ZrO 2 were 130 °C and 130 pC/N while those of the Sn-doped (K,Na)NbO 3 + ZrO 2 were 50 °C and 190 pC/N, respectively. These results suggest that the piezoelectric $d$ constant of (K,Na)NbO 3 -based multilayer ceramics with nickel inner electrodes can be increased by doping with Sn 2+ instead of Ca 2+ .