Theoretical study of the local distortions and the EPR parameters for VO2+ and Cu2+ centers in oxyfluoroborate glasses

Theoretical calculations of the local structures and the electron paramagnetic resonance (EPR) parameters for the impurities VO2+ and Cu2+ centers in oxyfluoroborate glasses (OFG) were performed by using the perturbation formulas of the EPR parameters for tetragonally compressed octahedral [VO6](8-) and tetragonally elongated octahedral [CuO6](10-) clusters, respectively. In the calculations, the required crystal-field (CF) parameters are estimated from the superposition model which enables correlation of the CF parameters and hence the EPR parameters with the tetragonal distortion (characterized by the relative tetragonal elongation (or compression) ratio tau along the C-4 axis) of [VO6](8-) (or [CuO6](10-)) cluster. Based on the calculations, the [VO6](8-) and [CuO6](10-) clusters are found to undergo the tetragonal compression (tau approximate to 1.7%) and elongation (tau approximate to 2.9%) along the C-4 axis, the signs of A(parallel to) and A(perpendicular to) for VO2+ and Cu2+ centers in OFG were also determined. The above theoretical approach on local structural properties would enhance the understanding of the structural properties for other oxide glasses with transition-metal (TM) dopants.

Automated summary

Theoretical calculations were conducted to determine the local structures and EPR parameters for VO2+ and Cu2+ impurities in oxyfluoroborate glasses. The study used perturbation formulas for EPR parameters and a superposition model for crystal-field parameters correlation with tetragonal distortion. The results indicated tetragonal compression and elongation for VO6 and CuO6 clusters in OFG, as well as determination of EPR parameter signs for VO2+ and Cu2+ centers.