Unusually soft ferroelectricity in (Ba _1-xSr _x)TiO ₃ ceramics

Temperature evolution of polarization versus electric field of (Ba _0.4Sr _0.6)TiO ₃ and (Ba _0.9Sr _0.1)TiO ₃ ceramics was investigated. Polarization characteristics of (Ba _0.9Sr _0.1)TiO ₃ belong to ferroelectrics with diffuse phase transition (DPT), while the ones of (Ba _0.4Sr _0.6)TiO ₃ are rather different. (Ba _0.4Sr _0.6)TiO ₃ ceramics display very soft ferroelectricity and extremely high dielectric tunability. The long-range ferroelectric ordering in (Ba _0.4Sr _0.6)TiO ₃ ceramics disappears completely below temperature T _m of maximum dielectric permittivity ε _m, which is different from normal DPT ferroelectrics. The special ferroelectric behavior is hypothesized to be attributed to random arrangements of the distorted TiO ₆ octahedra.