Lithium-sodium metaborate glasses: structural aspects and vitrification chemistry

Abstract Vibrational and devitrification techniques are employed to investigate the structure and glass-forming ability of x NaBO 2 · (1 − x )LiBO 2 glasses with 0 ⩽ x ⩽ 0.75. Alkali substitution is found to result in non-additive network changes due to the appearance of structures encountered in the newly discovered compound Li 3 NaB 4 O 8 ( x = 0.25). A decrease of T g with x is observed and attributed mainly to the partial suppression of the formation of tetrahedra-containing, β′- and γ-LiBO 2 -type, arrangements in the glass network. The dependence of the crystallization products on temperature is very pronounced for x = 0 and progressively diminishes for x → 0.25. This diminishment is taken to indicate that, upon increasing x (0 ⩽ x ⩽ 0.25), the structural rearrangements associated with the liquid-to-glass transition become less pronounced. In turn, alkali mixing in the system under investigation is correlated with decreasing melt ‘fragility’ and a less pronounced pathway glass morphology. Such remarks may be important in assessing the mixed alkali effect from a structural viewpoint, especially since they are compatible with earlier findings on lower modification borate analogs.