A Raman and MAS NMR study of mixed alkali Na-K and Na-Li aluminoborosilicate glasses

Structural studies of two types of aluminoborosilicate glasses (Na/K and Na/Li) using Raman and NMR spectroscopy are presented. Both types of glasses display a mixed alkali effect (MAE) according to electrical conductivity and T_g measurements. Concerning the glass structure and more particularly the silicate network, our results show that the MAE slightly affects the glass polymerization degree, which displays a maximum for intermediate Na/K and Na/Li range compositions. A non-linear variation of the BO₄/BO₃ ratio is also observed from ¹¹B MAS NMR. Moreover, our results demonstrate that potassium favors the formation of danburite-type rings in the glassy matrix and the assignment of the 1400 cm^-1 Raman band is revisited.