LITHIUM BERATE GLASSES - A QUANTITATIVE STUDY OF STRENGTH AND FRAGILITY

Methods for quantifying the strength/fragility of glass-forming system s are described, with particular reference to the alkali berates. One parameter used is the limiting slope of the log viscosity versus T/T plot as T approaches T, the temperature at which the viscosity is 10( 12) Pas. A comparison is made with Delta C-p/C-pl, the normalised chan ge in specific heat capacity at T-g, as an alternative measure of the degree of fragility in these glass-forming systems. Both approaches in dicate that increasing alkali oxide content results in increasing frag ility within the berate system, although anomalous correlations can re sult when different glassy systems are compared. The extent to which t he limiting viscosity slope and Delta C-p/C-pl probe different aspects of structural change and fragility is briefly explored.