High Quality Content by WIKIPEDIA articles! A chalcogenide glass (hard "ch" as in "chemistry") is a glass containing one or more chalcogenide elements. These are Group 16 in the periodic table e.g. sulfur, selenium or tellurium. Such glasses are covalently bonded materials and may be classified as network solids. In effect, the entire glass matrix acts like an infinitely bonded molecule. The classical chalcogenide glasses are strong glass-formers (mainly sulphur based ones) such as systems As-S, Ge-S possess glasses within large concentration regions. Glass forming abilities decrease with increasing molar weight of constituent elements i.e. S>Se>Te. Semiconducting properties of chalcogenide glasses were revealed in 1955 by B.T. Kolomiets and N.A. Gorunova from Ioffe Institute, USSR . This discovery initiated the numerous researches and applications of this new class of semiconducting materials.