Structural and energetic properties of domains in PbTiO3/SrTiO3 superlattices from first principles

We report first-principles calculations, within the density functional theory, on the structural and energetic properties of 180 degrees stripe domains in (PbTiO3)(n)/(SrTiO3)(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 SrTiO3 and PbTiO3 layers. Structurally, they display continuous rotation of polarization connecting 180 degrees 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.