Theoretical Studies of the Local Structure and EPR Parameters of Tetragonally Distorted Tetrahedral Cu2+ Sites in Phosphate Glasses

In this work, we theoretically investigate the local structure and electronic paramagnetic resonance (EPR) parameters (g-factors g i and A -constants A i , i = //, ⊥) of tetragonal Cu 2+ centers in phosphate glasses ( x CuO⋅(1 – x )[2P 2 O 5 ⋅Na 2 O] (0.5< x < 5 mol %)) with the aid of the three-order perturbation formulae of these parameters for 3d 9 ions in tetragonally distorted tetrahedra based on the cluster approach. In our calculations, both contributions to EPR parameters from the spin-orbit (SO) coupling interactions of the central Cu 2+ ions and the ligand orbital and SO coupling interactions are included. The crystal-field parameters related to the splitting of d-orbitals are calculated from the superposition model and the local structures of the studied Cu 2+ centers in the glasses. Based on the calculations, the local bond angle is found to be about 3.78° larger than that of the ideal tetrahedral site, resulting in a slightly compressed ligand tetrahedron. The relative contributions to the g-factors from the ligand orbital and SO coupling interactions are more important than those from the third-order perturbation terms. The theoretical results show good agreement with the experimental values. The signs and the less anisotropy (Δ A = | A // | – | A ⊥ | ) of A -constants for the tetrahedral Cu 2+ centers are discussed.