LITHIUM SODIUM METABORATE GLASSES - STRUCTURAL ASPECTS AND VITRIFICATION CHEMISTRY

Vibrational and devitrification techniques are employed to investigate the structure and glass-forming ability of x NaBO2 . (1 - x)LiBO2 glasses with 0 less-than-or-equal-to x less-than-or-equal-to 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 Li3NaB4O8 (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, beta'- and gamma-LiBO2-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 less-than-or-equal-to x less-than-or-equal-to 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.