Influence of Sulfur Ions on the Glass-Forming Ability and Structure of Silicate-Phosphate Glasses

The aim of the study was to analyze the structure of two groups of glasses: first sulfur-free from the SiO2-P2O5-K2O-MgO system and second sulfur-containing from the SiO2-P2O5-K2O-MgO-SO3 system with various network formers content in the form of P2O5 and SiO2. The sulfur speciation in the sulfur-bearing glasses was also determined. The sulfur-containing glasses were obtained under reducing conditions. The bulk composition of the glasses was confirmed by X-Ray Fluorescence Spectroscopy. The amorphous nature of the samples was verified using XRD analysis. The structure of the materials was studied with the 29Si and 31P MAS NMR and XAS spectroscopic techniques. It was found that the addition of sulfur increased the ability of glasses with higher amounts of P2O5 to form. XAS spectra demonstrate that S-bearing glasses contain sulfur in the reduced form as S2-. The 31P and 29Si MAS NMR spectra did not detect P-S and Si-S linkages.