Giant strain response and structure evolution in (Bi_0.5Na_0.5)_0.945-x(Bi_0.2Sr_0.7□_0.1)_xBa_0.055TiO₃ ceramics

The microstructure, electric-field-induced strain, polarization, and dielectric permittivity in (Bi_0.5Na_0.5)_0.945-x(Bi_0.2Sr_0.7□_0.1)_xBa_0.055TiO₃ (BNBT-xBST) (0≤x≤0.08) electroceramics are investigated. An irreversible transition from rhombohedral and monoclinic coexistence phase to single rhombohedral phase is indicated with the remnant strain S_r=0.330% at x=0. As the BST content increases, the ferroelectric order is disrupted resulting in a degradation of the remnant polarization, coercive field, and the ferroelectric-to-relaxor transition temperature (T_F-R). The coexistence of ferroelectric relaxor and ferroelectric phase is observed for the optimum composition x=0.02 at ambient temperature with a large strain of 0.428% at 60kV/cm (normalized strain S_max/E_max=713pm/V). The large strain is contributed by both ferroelectric domain reorientation behavior and the reversible relaxor to ferroelectric phase transition.