TOPOLOGY OF COVALENT NONCRYSTALLINE SOLIDS - SHORT-RANGE ORDER IN SEYGEXSB1-X-Y ALLOYS

The pronounced glass-forming tendencies of alloys of Se and Ge with Sb are discussed topologically in terms of the chemical bonds expected to be present in these materials. Using a simple consideration based on coordination numbers (m), and bond energies, the average number of near neighbours of each type expected to surround atom has been estimated. These average numbers of bonds have been used to estimate the cohesive energies (CE) of these glasses, assuming simple additivity of bond energies. A trial also has been made to explain the previously published data of threshold voltage (V-th), optical properties (E(04)) and glass transition temperature (T-g) of these materials; on the basis of our calculations the correlation between T-g and E(04) has been interpreted in terms of a proposed fluidity equation for covalent liquids with 2.3 less than or equal to m less than or equal to 2.49.