Theory of PbTiO3, BaTiO3, and SrTiO3 Surfaces

TL;DR

This study uses first-principles calculations to analyze the atomic and electronic structures of (001) surfaces in PbTiO3, BaTiO3, and SrTiO3, revealing differences in surface stability, ferroelectric behavior, and surface relaxation energies.

Contribution

It provides a detailed comparison of surface properties and ferroelectric effects in three perovskite materials, highlighting the impact of covalent bonding and surface termination on stability.

Findings

BaTiO3 and SrTiO3 surfaces are thermodynamically stable with both terminations.

PbTiO3 surface stability is limited to PbO termination.

Surface relaxation energies are significantly larger than bulk ferroelectric well depths.

Abstract

First-principles total-energy calculations are carried out for (001) surfaces of the cubic perovskite ATiO3 compounds PbTiO3, BaTiO3, and SrTiO3. Both AO-terminated and TiO2-terminated surfaces are considered, and fully-relaxed atomic configurations are determined. In general, BaTiO3 and SrTiO3 are found to have a rather similar behavior, while PbTiO3 is different in many respects because of the partially covalent character of the Pb-O bonds. PbTiO3 and BaTiO3 are ferroelectrics, and the influence of the surface upon the ferroelectric distortions is studied for the case of a tetragonal ferroelectric distortion parallel to the surface. The surface relaxation energies are found to be substantial, i.e., many times larger than the bulk ferroelectric well depth. Nevertheless, the influence of the surface upon the ferroelectric order parameter is modest, and is qualitatively as well as quantitatively different for the two materials. Surface energies and electronic properties are also computed. It is found that for BaTiO3 and SrTiO3 surfaces, both AO-terminated and TiO2-terminated surfaces can be thermodynamically stable, whereas for PbTiO3 only the PbO surface termination is stable.