Physical properties and MAS-NMR studies of titanium phosphate-based glasses

In this study, for a series phosphate-based glasses ((P2O5)0.45(CaO)0.3(Na2O)0.25−x(TiO2)x, 0 ≤ x ≤ 0.15), their degradation, ion release, surface and thermal properties have been determined. The results show that adding TiO2 was associated with a significant increase in density and glass transition temperature, but a decrease in degradation rate and ion release. 31P solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) showed that the local structure of the glasses changes with increasing TiO2 content. As TiO2 is incorporated into the glass, the phosphate connectivity increases as Q1 units transform to Q2, confirming that an increase in the nominal TiO2 content correlates unequivocally with an increase in glass stability. As reported for titania–silica gels, Ti4+ is clearly adopting a network former role in these phosphate-based glasses. 23Na MAS-NMR results corroborate this phenomenon with a marked upfield trend of the 23Na isotropic chemical shift suggesting that the local Na–O bond distances are decreasing within a more condensed glass network upon increased incorporation of TiO2.