Large piezoelectric effect of (Ba,Ca)TiO3-xBa(Sn,Ti)O3 lead-free ceramics

(Ba0.9Ca0.1)TiO3-xBa(Sn0.2Ti0.8)O-3 ceramics (abbreviated as BCT-xBST) were obtained and the relationships among phase structure, energy barrier and piezoelectric properties were studied. Their phase structures are tetragonal (T)-orthorhombic (0) coexistence at 0.20 <= x <= 0.40, rhombohedral (R)-O-T multiphase coexistence at x=0.45 and R phase or R-cubic (C) two-phase coexistence at 0.50 <= x <= 0.60, respectively. The energy barrier of polarization rotations and extension for R-O and O-T two-phase coexistence as well as R-O-T multiphase one was analyzed by the conservation law of energy and Landau-Devonshire theory. Because of extremely low energy barrier for polarization rotation and extension, high piezoelectric coefficients d(33) = 630 pC/N, k(p) = 0.52 and the lower E-c = 0.81 kV/cm were achieved at x = 0.45 which has R-O-T multiphase coexistence. These results confirm that the low energy barrier for polarization rotation and extension at R-O-T multiphase coexistence composition is beneficial to enhance the d(33) value. The high piezoelectric property also indicates that BCT-xBST ceramics are a promising candidate for lead-free piezoelectric ceramics. (C) 2015 Elsevier Ltd. All rights reserved.