Electrical conductivity and 11B NMR studies of sodium borosilicate glasses

A large number of compositions within the SiO2–NaO2–B2O3 (SNB) ternary glass system were investigated by various complementary techniques. Impedance spectroscopy was used to determine the parameters related to sodium ion diffusion in the glass structure; high-field boron NMR measurements on a series of samples identified and quantified the boron coordination as a function of the composition; exhaustive DTA measurements gave the glass transition temperature for all the compositions studied. Based on these results we demonstrate that the activation energy of sodium ion diffusion is closely related to the boron coordination number and involves two types of structural motifs: one corresponding to the sodium associated to non-bridging oxygen atoms, and the other to sodium compensating BIV motif. We also show that simple DTA measurements of the glass transition temperature can be used to define structural domains within this ternary composition range.