Orthorhombic-pseudocubic phase transition and piezoelectric properties of (Na0.5K0.5)(Nb1-xSbx)-SrZrO3 ceramics

Abstract

0.96(Na0.5K0.5)(Nb1-xSbx)-0.04SrZrO(3) ceramics with 0.0 <= x <= 0.06 were well sintered at 1060 degrees C for 6 hours without a secondary phase. Orthorhombic-tetragonal transition temperature (TO-T) and Curie temperature (T-C) decreased with the addition of Sb2O5. The decrease in T-C was considerable compared to that in TO-T, and thus the tetragonal phase zone disappeared when x exceeded 0.03. Therefore, a broad peak for orthorhombic-pseudocubic transition as opposed to that for orthorhombic-tetragonal transition appeared at 115 degrees C-78.2 degrees C for specimens with 0.04 <= x <= 0.06. An orthorhombic structure was observed for specimens with x <= 0.03. However, the polymorphic phase boundary structure containing orthorhombic and pseudocubic structures was formed for the specimens 0.04 <= x <= 0.06. Furthermore, a specimen with x <= 0.055 exhibited a large piezoelectric strain constant of 325 pC/N, indicating that the coexistence of orthorhombic and pseudocubic structures could improve the piezoelectric properties of (Na0.5K0.5)NbO3-based lead-free piezoelectric ceramics.