Structural transition and dielectric response of an epitaxially strained BaTiO3 SrTiO3 superlattice: A first-principles study

We determine the structure and static dielectric response of the BaTiO31unitcell SrTiO31unitcell (BTO/STO) superlattice as a function of epitaxial strain using first-principles density functional theory (DFT) calculations based on pseudopotentials and a plane-wave basis. We find a structural transition from the tetragonal phase at compressive strains to the monoclinic phase at tensile strains, with a nonzero in-plane component of polarization in the monoclinic phase as its order parameter. For the stable structures determined as a function of in-plane strain, we obtained optical phonon frequencies, Born effective charges and static dielectric constants using DFT linear response. Our calculations predict a large zero-temperature dielectric response with a strong anisotropy, whose origin is traced to soft phonons of the superlattice.