Studies on the local structures and spin Hamiltonian parameters for the rhombic Nb⁴⁺ centers in MO₂ (M = Sn, Ti and Ge) crystals

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

Corresponding author: shaoyi_wu@163.com

Received: 14 April 2010
Accepted: 29 November 2010
Published online: 28 January 2011

Abstract

The local structures and the spin Hamiltonian parameters for the substitutional Nb⁴⁺ centers in MO₂ (M = Sn, Ti and Ge) crystals are theoretically studied using the perturbation formulas of these parameters for a 4d¹ ion in a rhombically compressed octahedron. The above Nb⁴⁺ centers are found to experience the Jahn-Teller distortions, characteristic of the relative axial compressions (~ 0.01–0.02 Å) and the non-axial (planar) angular increases (~ 3°). As a result, the ligand octahedra are transformed from original elongation on host tetravalent cation sites to compression in the impurity centers, with additional non-axial distortions smaller than those in the hosts. The influences of the Jahn-Teller distortions and the ligand orbital contributions are also analyzed.