29Si MAS NMR studies of alkali silicate oxynitride glasses

Abstract

Magic angle spinning nuclear magnetic resonance (MAS NMR) has been applied to study the structural effect of nitrogen incorporation into glasses. Analysis of the 29Si NMR spectra in binary alkali silicate glasses has revealed the coexistence of at least three structural units for all compositions, though the Q^n distribudon is not too far from "binary". Addition of nitride to the system SiO2-Na2O leads to a progressive substitution of bridging oxygen by nitrogen atoms which are linked to three silicon tetrahedra. Numerical evaluation of the spectra and exact chemical analysis of the glasses have made it possible to relate the mean value for the number of Si-N bonds per tetrahedral unit quantitatively to the Si3N4 content. 23Na MAS NMR spectra are not affected by the nitrogen. Data obtained from glasses in the system SiO2-Na2O-CaO-Si3N4 have been discussed in the same way.