Mixed Ising-Bloch-N\'eel Character to 180 $^{\circ}$ Ferroelectric Domain Walls

Ferroelectric 180-degree domain walls are well-known to be predominantly Ising-like. Using density functional theory, and molecular dynamics simulations, the 180 degree 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 N\'eel-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.