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

(Ba0.9Ca0.1)TiO3–xBa(Sn0.2Ti0.8)O3 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 (O) 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 d33 = 630 pC/N, kp = 0.52 and the lower EC = 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 d33 value. The high piezoelectric property also indicates that BCT–xBST ceramics are a promising candidate for lead-free piezoelectric ceramics.