In order to study the way in which the modifying sodium cations interact with the network in (Na//2O)//x(Teo//2)//1// minus //x glasses, we have probed the sodium sites using the dynamic angle spinning NMR experiment. By performing this experiment at two different magnetic field strengths, we extract the chemical shift and quadrupole coupling parameters, which we relate to the glass structure with the aid of an empirical model. Our results suggest that the sodium coordination changes from about six, at low modifier concentrations, to about five, at high concentrations. This decrease is not monotonic, however; it is relatively independent of concentration from 10 to about 18 mol %, at which point it begins to decrease. We interpret this change as due to the onset of formation of significant numbers of nonbridging oxygen. (Author abstract) 29 Refs.
Tagg, S.L. Youngman, R.E. Zwanziger, J.W.