Theoretical studies of the local structures and the g factors for the tetragonal Ti3+-Vo centers in BaTiO3 bulks and thin films

The local structures and the EPR g factors g║ and g┴ are theoretically studied for the tetragonal Ti3+-Vo centers in BaTiO3 bulks and thin films using the perturbation formulas of the g factors for a 3d1 ion in tetragonally elongated octahedra and compressed tetrahedra, respectively, based on the cluster approach. For the Ti3+-Vo center in BaTiO3 bulks, the impurity Ti3+ suffers the displacement away from the oxygen vacancy Vo by about 0.15 Å along the C4 axis due to the electrostatic repulsion of the Vo. Nevertheless, the Ti3+-Vo center in BaTiO3 thin films may exhibit the tetragonally compressed tetrahedron, characterized by the bond angle 55.88° larger than that (≈54.74°) of an ideal tetrahedron. The quite different g factors (especially g anisotropies Δg = g║ − g┴) for the two kinds of samples are discussed, in view of the dissimilar bonding or coordination environments (i.e., incomplete bonding in the thin films may lead to the lower coordination number).