Mixed Bloch-Néel-Ising character of 180°ferroelectric domain walls

Ferroelectric 180°domain walls are well-known to be predominantly Ising-like. Using density functional theory, and molecular dynamics simulations, the 180°domain walls in prototypical ferroelectrics lead titanate (PbTiO3) and lithium niobate (LiNbO3) are shown to have mixed character; while predominantly Ising-like, they also manifest some Bloch- and Néel-like character. Phase-field calculations show that such mixed wall character can be dramatically enhanced in nanoscale thin film heterostructures such as BaTiO3 / SrTiO3, where the internal wall structure can form polarization vortices. Such mixed character walls can be expected to exhibit dynamical wall properties distinct from pure Ising walls.