VISCOSITY OF CHALCOGENIDE GLASS-FORMING LIQUIDS - AN ANOMALY IN THE STRONG AND FRAGILE CLASSIFICATION

High purity chalcogenide glasses with an average coordination number, [r], between 2 and 2.8 were prepared by vacuum melting of pre-distille d samples in the Ge-Se binary and Ge-Sb-Se ternary systems. Viscometry and scanning calorimetry were performed to understand the nature of t he property thresholds observed with respect to [r] in these glass-for ming systems. There is a lack of correlation between viscosity-based a nd heat capacity-based classifications of strong and fragile Liquids i n the overconstrained region of these glass-forming systems. An argume nt based on Adam-Gibbs equation and mode decoupling is put forward for the observation of the anomaly.