A chalcogenide glass (hard "ch" as in "chemistry") is a glass containing one or more chalcogenide elements (Group VI in the periodic table e.g. sulfur, selenium or tellurium) as a substantial constituent. They are covalently bonded materials and may be classified as molecular solids, that is to say the entire glass matrix may be considered as an infinitely bonded molecule.
Applications
The modern technological applications of chalcogenide glasses are widespread specifically as mouldable infrared optics including lenses, and infrared optical fibers as these materials transmit across the full range of the infrared regime of the electromagnetic spectrum. The physical properties of chalcogenide glasses (High refractive index, low phonon energy) also make them ideal for incorporation into laser and other active devices when doped with rare earth ions. Some chalcogenide materials experience thermally driven amorphous crystalline phase changes, enabling the encoding of binary information on thin films of chalcogenides, forming the basis of rewritable optical dics 1 and non-volatile memory devices such as PRAM. Examples of such Phase change materials are GeSbTe and AgInSbTe. In optical discs, the phase change layer is usually sandwiched between dielectric layers of ZnS-SiO2, sometimes with a layer of a crystallization promoting film.citation needed Other less common such materials are InSe, SbSe, SbTe, InSbSe, InSbTe, GeSbSe, GeSbTeSe, and AgInSbSeTe.2
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