Glass formation and transition temperatures in sodium and lithium borate and aluminoborate melts up to 72 mol.% alkali

Abstract

We report continuous glass formation and glass transition temperatures T g for the pseudo-binary systems xM 2O (1 − x) (0.87B 2O 30.13Al 2O 3) to x = 0.675 for M = Na and 0.575 for M = Li. A dependence of both T g and glass-forming range on starting materials is found at high alkali contents, and attributed to retained CO 2. Maxima in T g for both binary and pseudo-binary systems are quantitatively described in terms of two effects: (i) creation of 4-coordinated borons (increasing T g), and (ii) creation of non-bridging [BO 3] oxygens (decreasing T g. To first approximation we find the latter imparting a stronger effect on T g.