A density functional theory study of oxygen diffusion in LaAlO3 and SrTiO3

Chemical bonding-scale aspects of oxygen diffusion in candidate high-k gate oxides LaAlO3 and SrTiO3 were investigated from first-principles, within density functional theory. Relaxed atomic positions, total energies and electron density maps were calculated along oxygen vacancy migration paths, for 2 2 2 supercells. Quite low activation energies were obtained (similar to 0.6 eV, in agreement with experiment) for both compounds. Microscopic factors involved in the diffusion process were investigated further by a topological analysis of the electron density, according to Bader's "Atoms in Molecules" theory. At the diffusion saddle point, transitory states such as O- or atomic oxygen may explain the activation energy low values. Finally, we propose the use of energy density variation maps, as a way to identify parts of the density that contribute to increase (resp. decrease) the diffusion barrier. By extension, this type of tool may help to gain insight in phenomena such as phase transitions, and constitute the basis of an "electron density engineering" for materials design and optimization. (C) 2008 Elsevier B.V. All rights reserved.