The effect which an H impurity had upon the geometry and electronic structure of the crystal was considered. A quantum-chemical method which was based upon the Hartree-Fock formalism, and the periodic large unit-cell model, was used. An analysis of the results showed that the interstitial H impurity bonded to one of the O atoms which formed the so-called O-H group. At equilibrium, the O-H distances were equal to 0.089 and 0.104nm for the cubic and orthorhombic lattices, respectively. In the cubic phase, the computed relaxation energy in the vicinity of the O-H group was found to be equal to 1.1eV, and the atomic displacements generally obeyed the Coulomb law. The negatively charged O atoms thus moved outwards from the defective region, by about 0.009nm, while the positively charged Ti and Ca atoms moved towards the defective region by about 0.005 and 0.001nm, respectively. A similar effect was observed in orthorhombic lattices doped with H atoms. Various O positions in the orthorhombic structure were considered for O-H bond creation. The computed relaxation energies of the atomic displacements in this structure were equal to 2.3 or 2.1eV; depending upon the crystallographic type of the bonding O atom.

The H Atom in CaTiO3 - Structure and Electronic Properties. M.Castillo, C.Velasco, A.Stashans: Philosophical Magazine, 2003, 83[15], 1845-54