Sodium distribution in sodium tellurite glasses probed with spin-echo NMR

Abstract

We present results on the spatial distribution of sodium cations in sodium tellurite glasses as a function of sodium oxide content, obtained using a spin-echo NMR experiment. Glasses were studied with sodium oxide content ranging from 10 to 30 mol %. From the decay rate of the spin echo we infer the proximity of sodium nuclei at each composition. We found that at low sodium oxide contents the data are well modeled by a random distribution of sodium ions, with a closest approach distance of 3.2 Angstrom in correspondence with sodium tellurite crystal structures. At higher sodium oxide contents, however, the data agree with sodium distributions that have extensive intermediate range order, on length scales of at least 10 Angstrom. This ordering is most pronounced at 20% sodium oxide content, the composition at which this glass has been claimed to have maximum stability against devitrification.