| Abstract Scope |
Infrared and Raman spectroscopy reveal significant differences in the near and intermediate range order of alkali borosilicate glasses, including in the interconnectivities of borate and silicate units. For low alkali borosilicate glasses, changes in the quenching rate reflect on a different degree of mixing between borate and silicate units, with increasingly more homonuclear bonds for low and more mixed B-O-Si bonds for high fictive temperatures. 2D correlation NMR showed that tetrahedral borate groups avoid bonding to silicate over other borate groups. However, for higher alkali glasses with a significant number of non-bridging oxygen atoms, silicate and borate tetrahedra do not avoid direct linkages. Heat treatment, or the addition of rare earth or transition metal oxides can enhance preferential bonding in low alkali glasses and induce clustering and even visible phase separation. Changing the alkali oxide from Li to Cs, can significantly alter the connectivity of the borate and silicate sub-networks. |