First-principles simulations on the structural and energetic properties of domains in PbTiO$_3$/SrTiO$_3$ superlattices

Abstract: We report first-principles calculations, within the density functional theory, on the structural and energetic properties of 180$^\circ$ stripe domains in (PbTiO${3}$)${n}$/(SrTiO${3}$)${n}$ superlattices. For the explored periodicities ($n$=3 and 6) we find that the polydomain structures compete in energy with the monodomain phases. Our results suggest the progressive transition, as a function of $n$, from a strong to a weak electrostatic coupling regime between the SrTiO${3}$ and PbTiO${3}$ layers. Structurally, they display continuous rotation of polarization connecting 180$^\circ$ domains. A large offset between [100] atomic rows across the domain wall and huge strain gradients are observed. The domain wall energy is very isotropic, depending very weakly on the stripe orientation.