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

¹ Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, P.R. China
² International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, P.R. China

^a e-mail: zhihongzhang723@163.com

Received: 20 May 2011
Revised: 8 July 2011
Accepted: 17 August 2011
Published online: 28 September 2011

Abstract

The local structures and the EPR g factors g_║ and g_┴ are theoretically studied for the tetragonal Ti³⁺-V_o 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⁺-V_o center in BaTiO₃ bulks, the impurity Ti³⁺ suffers the displacement away from the oxygen vacancy V_o by about 0.15 Å along the C₄ axis due to the electrostatic repulsion of the V_o. Nevertheless, the Ti³⁺-V_o 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).