Relationship between the Average Coordination Number and Properties of Chalconitride Glasses

Chalconitride glasses obtained by doping Ge-As-Se and Ge-S chalcogenide glass systems with Si₃N₄ (0.35 and 0.50 wt%) have been studied; these glasses have been doped with Si₃N₄ to improve their thermal and mechanical prop-erties. The glasses have been melted under vacuum in sealed silica ampoules, quenched in air, and subsequently annealed. Measured properties include the transition temperature ( T _g), microhardness ( H _v), and thermal expansion coefficient (α). The effect of Si₃N₄ doping is system depen-dent. The concept of average coordination number () is used to explain this dependence. For the glasses in the chal-cogen-rich region, a greater increase in thermal and mechanical properties with Si₃N₄ doping is assigned to the fact that both the introduction of silicon and the substitution of nitrogen for chalcogens enhance the degree of crosslinking within the substructures. However, for the glasses in the chalcogen-deficient region, extra silicon atoms that are in-troduced with Si₃N₄ doping are not helpful in further crosslinking the network, because of the deficiency in the bridging chalcogens. A slight increase in T _g with increasing , in the case of chalcogen deficiency, might result from the "wrong-bond effect," which provides some additional crosslinking in connections of the networked island sub-structural units.