Chalcogenide glass
![A CD-RW (CD). Amorphous chalcogenide materials form the basis of re-writable CD and DVD solid-state memory technology.[2]](/Images/godic/202501/03/CD-RW_bottom1022.jpg")
Chalcogenide glass (hard "ch" as in "chemistry") is a glass containing one or more chalcogenide elements sulfur, selenium and tellurium, but excluding oxygen. Such glasses are covalently bonded materials and may be classified as covalent network solids. Polonium is a chalcogenide but is not used because of its strong radioactivity and high price. Chalcogenide materials behave rather differently from oxides, in particular their lower band gaps contribute to very dissimilar optical and electrical properties.