Surface and ferroelectric properties of PbTiO3 thin films were investigated using an interatomic potential approach with parameters determined from first-principles calculations. It was shown that a model developed for the bulk describes properly the surface properties of PbTiO3. In particular, the antiferrodistortive surface reconstruction, observed with X-ray scattering, was correctly reproduced as a result of the change in the balance of long-range Coulombic and short-range interactions at the surface. The effects of the surface reconstruction on the ferroelectric properties of ultra-thin films were investigated. Under the imposed open-circuit electrical boundary conditions, the model gives a critical thickness for the ferroelectricity of four unit cells. The surface layer, which formed the antiferrodistortive reconstruction, participated in the ferroelectricity. A decrease in the tetragonality of the films led to the stabilization of a phase with non-vanishing in-plane polarization. A peculiar effect of the surface reconstruction on the in-plane polarization profile was found.

Surface Reconstruction and Ferroelectricity in PbTiO3 Thin Films. M.Sepliarsky, M.G.Stachiotti, R.L.Migoni: Physical Review B, 2005, 72[1], 014110 (6pp)