Propensity for spontaneous relaxor-ferroelectric transition in quenched (Na_1/2Bi_1/2)TiO₃-BaTiO₃ compositions

Recently, quenching lead-free non-ergodic relaxor Na_1/2Bi_1/2TiO₃-BaTiO₃ (NBT-BT) materials has been reported to increase the thermal depolarization temperature and enhance the lattice distortion. Driven by the conjecture that enhanced lattice distortion is typically associated with the onset of ferroelectric order, two non-ergodic relaxor NBT-BT compositions at the morphotropic phase boundary were investigated. As evident from the temperature-dependent permittivity, both compositions exhibit a stabilization of ferroelectric order upon quenching. An increase in the depolarization temperature by 40–60 °C is observed. Moreover, the composition with higher tetragonality undergoes a spontaneous relaxor-ferroelectric transition upon quenching. Annealing in oxygen atmosphere is shown to revert back the quenching-induced ferroelectric order to the relaxor state.