RELATIONSHIP BETWEEN THE AVERAGE COORDINATION-NUMBER AND PROPERTIES OF CHALCONITRIDE CLASSES

Chalconitride glasses obtained by doping Ge-As-Se and Ge-S chalcogenid e glass systems with Si3N4 (0.35 and 0.50 Wt%) have been studied; thes e glasses have been doped with Si3N4 to improve their thermal and mech anical properties. 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 (alpha). The effect of Si3N4 do ping is system dependent. The concept of average coordination number ( <r>) is used to explain this dependence. For the glasses in the chalco gen-rich region, a greater increase in thermal and mechanical properti es with Si3N4 doping is assigned to the fact that both the introductio n of silicon and the substitution of nitrogen for chalcogens enhance t he degree of crosslinking within the substructures. However, for the g lasses in the chalcogen-deficient region, extra silicon atoms that are introduced with Si3N4 doping are not helpful in further crosslinking the network, because of the deficiency in the bridging chalcogens. A s light increase in T-g with increasing <r>, in the case of chalcogen de ficiency, might result from the ''wrong-bond effect,'' which provides some additional crosslinking in connections of the networked island su bstructural units.