First principles investigation of polarisation at interfaces in multilayered strontium titanate

One of the main factors which affects the bulk properties of multilayered perovskites is the atomic structure at the interface between different types of layers. We have applied Density Functional Perturbation Theory to investigate the polarisation properties of interfaces in two different phases of nonstoichiometric SrTiO3, the Ruddlesden-Poppper and Magnéli phases. Our calculated Born effective charge tensors and high-frequency dielectric constants are compared for each type of interface and bulk SrTiO 3. For both phases, we find that the presence of the interface introduces huge anisotropy into the Born effective charges of the participating ions. We attempt to interpret our results using a simplified tight binding model and analyse the limitations of such an approach.