Theoretical investigation of the Ruddlesden-Popper compounds Sr(n+1)Ti(n)O3(n+1) (n=1-3)

We have performed a theoretical study of the atomic and electronic structur e of the four compounds Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10 and SrTiO3, by a total -energy semiempirical Hartree-Fock method. We show that the intercalation o f SrO layers in the perovskite structure of SrTiO3 induces lattice distorti ons and modifications of the electronic structure, which are mainly localiz ed close to the stoichiometry defect. They include a contraction of the SrO -TiO2 interplanar distance, a rumpling of the adjacent layers and an increa se in the ionicity of the Sr-O bond. As the index n increases, the compound s Srn+1TinO3n+1 become more and more unstable with respect to phase dissoci ation and we predict a limit of stability for n approximate to 3.