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Chalcogenide glass is a glass containing one or more chalcogens. Such glasses are covalently bonded materials and may be classified as covalent network solids. Polonium is also a chalcogen but is not used because of its strong radioactivity. Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.
The classical chalcogenide glasses are strong glass-formers and possess glasses within large concentration regions. Glass-forming abilities decrease with increasing molar weight of constituent elements; i.e., S > Se > Te.
Chalcogenide compounds such as AgInSbTe and GeSbTe are used in rewritable optical disks and phase-change memory devices. They are fragile glass-formers: by controlling heating and annealing , they can be switched between an amorphous and a crystalline state, thereby changing their optical and electrical properties and allowing the storage of information.