Superposition model analysis of the short-range ordering for Mn2+in oxide glasses

The superposition model is employed to account for the fine-structure parameters for Mn2+in oxide glasses determined recently by computer simulations of g=2.0 and g=4.3 resonances. Analytic expressions relating distributions of the fine-structure parameters D and E to distributions of ligand coordinates are obtained for sixfold and fourfold coordinations of Mn2+. Quantitative estimates are made of mean distortion parameters and root-mean-square variations of interatomic distances and angles in the environment of Mn2+. It is shown that both the mean distortions from cubic symmetry and the degree of short-range disorder are considerably smaller for the g=2.0 sites than for the g=4.3 sites. A possibility of attributing the g=2.0 and g=4.3 resonances to Mn2+ions substituting respectively for network modifiers and network formers in the oxide glasses is discussed.