TABLE OF CONTENTS The term chalcogenide refers to the elements in the VIA column of the periodic table, i.e., O, S, Se, Te, and Po. Since the isotopes of polonium are radioactive, no significant studies have been reported using polonium in glasses. If we consider the other four chalcogenides, we find that oxygen differs from the others in that (a) it is a gas at room temperature and (b) oxygen exists as individual O 2 molecules, while S and Se melts contain rings and chains which can interact to form a vitreous structure. Melts of tellurium, which is much more difficult to form as a glass, also contain chains, with a structure similar to that of molten Se. It follows that the term chalcogenide glasses is limited to compositions containing S, Se, and/or Te. While many other elements can be added to these glasses, the primary chalcogenide glasses contain one or more of these three elements, along with elements from groups IVA (Si, Ge, Sn) and VA (P, As, Sb, Bi). If the glasses also contain a halide, they are commonly termed chalcohalide glasses.
Structural models for these glasses are based on the high degree of covalent bonding between chalcogenide atoms. Sulfur melts contain 8-membered rings at low temperatures, with covalent bonding between adjacent sulfur atoms. These rings begin to convert to extremely long chains of S atoms at temperatures above 160 C, with chain lengths exceeding 10 6 atoms. Molten Se contains somewhat...
