Large piezoelectricity and dielectric permittivity in BaTiO ₃-xBaSnO ₃ system: The role of phase coexisting

We report ultrahigh dielectric and piezoelectric properties in BaTiO ₃-xBaSnO ₃ ceramics at its quasi-quadruple point, a point where four phases (Cubic-Tetragonal-Orthorhombic- Rhombohedral) nearly coexist together in the temperature-composition phase diagram. At this point, dielectric permittivity reaches ∼75000, a 6-7-fold increase compared with that of pure BaTiO ₃ at its Curie point; the piezoelectric coefficient d ₃₃ reaches 697 pC/N, 5 times higher than that of pure BaTiO ₃. Also, a quasi-quadruple point system exhibits double morphotropic phase boundaries, which can be used to reduce the temperature and composition sensitivity of its high piezoelectric properties. A Landau-Devonshire model shows that four-phase coexisting leading to minimizing energy barriers for both polarization rotation and extension might be the origin of giant dielectric and piezoelectric properties around this point.