Crystal structures and domain patterns of unpoled and poled Bi0.5(Na0.78K0.22)0.5TiO3 ceramics by TEM

• We first reported the domain patterns of Bi0.5(Na0.78K0.22)0.5TiO3 ceramics.
• TEM images exhibited the difference of domain width between poled and unpoled sample.
• The crystal structures of the lamellar domains were determined to be P4bm.
• The poling induced domain growth and enhanced the stability of ferroelectricity.

The crystal structures and domain patterns of unpoled and poled Bi0.5(Na0.78K0.22)0.5TiO3 ceramics fabricated using a solid-state reaction, were studied using transmission electron microscopy (TEM). The temperature dependence of the dielectric permittivity and P–E hysteresis loop curve were also investigated. While the poled sample exhibited an obvious ferroelectric property in the dielectric behavior and P–E loop; the unpoled sample showed only a trace of depolarization temperature. Both poled and unpoled samples exhibited lamellar domain structures, which possessed wide domains (~100 nm thick) in the poled sample and narrow domains in the unpoled sample. The crystal structures of the lamellar domains were determined to be P4bm. The poling process induced domain growth and enhanced the stability of ferroelectricity; this consequently led to an irreversible electric-field-induced phase transition, which is a feature of the non-ergodic relaxor.