Theoretical Studies of the Electron Paramagnetic Resonance Parameters and Local Structure for VO²⁺ in Oxyfluoroborate Glasses

The electron paramagnetic resonance parameters (g factors g _‖, g _⊥ and hyperfine structure constants A _‖, A _⊥) of a tetragonal V⁴⁺ center in oxyfluoroborate glasses (20Li₂O-10Li₂F₂-70B₂O₃) are theoretically investigated by using the perturbation formulas for a 3d¹ ion in tetragonally compressed octahedra. The calculated results are in good agreement with the experimental data. Local structure parameters of [VO₆]^8- clusters are obtained from the calculation (i.e., R_‖ ≈ 1.74 Å and R_⊥ ≈ 1.985 Å for the metal-ligand distances parallel and perpendicular to the C₄ axis, respectively). It is shown that the local structure around the V⁴⁺ ion possesses a compressed tetragonal distortion along C ₄ axis. The signs of the hyperfine structure constants A‖ and A _⊥ for V⁴⁺ centers in oxyfluoroborate glasses were also suggested in the discussion. (paper)