Studies on the defect structures for two Rh2+ centers in LiD

The defect structures for two Rh2+ centers {A} and {O} in LiD are theoretically studied by analyzing their experimental EPR parameters, based on the perturbation formulas of these parameters for a 4d7 ion with low spin (S = 1/2) in tetragonally compressed octahedra and orthorhombically elongated octahedra. Center {A} can be attributed to the substitutional Rh2+ at the Li+ site, associated with the next nearest neighbouring (nnn) Li+ vacancy VLi along [0 0 1] (or C4) axis as the compensator. In this center, the intervening ligand D- in Rh2+ and the VLi is found to shift towards Rh2+ by an amount ΔZA ∼ 0.01 A due to the electrostatic repulsion of the VLi. Center {O} is assigned to the elongation δ ∼ 0.072 A of the ligand octahedron along [0 0 1] axis due to the Jahn-Teller effect, associated with one nnn VLi along [1 0 0] (or X) axis. The intervening ligand may also suffer a displacement ΔXO ∼ 0.11 A towards Rh2+. In the calculations of the hyperfine structure constants, the reduction factors H (∼0.49 and 0.93) due to the Rh2+ 4d-5s orbital admixture are obtained for centers {A} and {O}