Small-Signal Permittivity of the Stationary (100)-180° Domain Wall in BaTiO 3

The small-signal permittivity of the (100)-type 180° domain wall in BaTiO 3 is calculated relative to the signal-domain permittivity according to a previously-reported microscopic model of 180° domain walls in BaTiO 3 . A perturbation approach is developed which makes use of the known zero-field solutions of this domain wall and the single domain. It is found that the (100) domain-wall permittivity is about 6\(1/2\)-times larger than the single-domain permittivity, and there are two reasons for this effect; First, the internal fields and polarizabilities of the ions in the wall region differ from the single-domain values; and second, the presence of a field lowers the domain-wall symmetry promoting the polarization of the Ba and O b ions on the (100) domain-wall plane. The dominant contribution to the enhanced domain-wall permittivity is the induced Ba and O b polarizations.