Coordination environment of fluorine in the CaO-SiO2-CaF2 glasses bearing Na2O:: A solid-state 19F MAS NMR study

The coordination environment of fluorine in the CaO-SiO2-CaF2-Na2O glasses has been measured by F-19 MAS NMR over a wide composition range including the similar compositions to those of mould fluxes so as to determine the composition dependence of the coordination environment of F-. Most of F- are fourfold-coordinated by Ca2+ for the samples having the value of n(Na)/(n(Na)+n(Ca))less than or equal to0.3, where n represents the mole fraction of each cation. On the other hand, the samples having the value of n(Na)(n(Na)+n(Ca))greater than or equal to0.4 contain F- coordinated with both Na+ and Ca+ and F- sixfold-coordinated by Na+.