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Chalcogenide glass
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Chalcogenide glass
Chalcogenide glass (pronounced hard ch as in chemistry) is a glass containing one or more heavy chalcogens (sulfur, selenium or tellurium; polonium is also a heavy chalcogen but too radioactive to use). 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 (mainly sulfur-based ones such as As-S or Ge-S) 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 (cooling), they can be switched between an amorphous (glassy) and a crystalline state, thereby changing their optical and electrical properties and allowing the storage of information.
Most stable binary chalcogenide glasses are compounds of a chalcogen and a group 14 or 15 element and may be formed in a wide range of atomic ratios. Ternary glasses are also known.
Not all chalcogenide compositions exist in glassy form, though it is possible to find materials with which these non-glass-forming compositions can be alloyed in order to form a glass. An example of this is gallium sulphide-based glasses. Gallium(III) sulphide on its own is not a known glass former; however, with sodium or lanthanum sulphides it forms a glass, gallium lanthanum sulphide (GLS).
Up until recently, chalcogenide glasses (ChGs) were believed to be predominantly covalently bonded materials and classified as covalent network solids. A most recent and extremely comprehensive university study of more than 265 different ChG elemental compositions, representing 40 different elemental families now shows that the vast majority of chalcogenide glasses are more accurately defined as being predominantly bonded by the weaker van der Waals forces of atomic physics and more accurately classified as van der Waals network solids. They are not exclusively bonded by these weaker vdW forces, and do exhibit varying percentages of covalency, based upon their specific chemical makeup.
Uses include infrared detectors, mouldable infrared optics such as lenses, and infrared optical fibers, with the main advantage being that these materials transmit across a wide range of the infrared electromagnetic spectrum.
The physical properties of chalcogenide glasses (high refractive index, low phonon energy, high nonlinearity) also make them ideal for incorporation into lasers, planar optics, photonic integrated circuits, and other active devices especially if doped with rare-earth element ions. Some chalcogenide glasses exhibit several non-linear optical effects such as photon-induced refraction, and electron-induced permittivity modification
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Chalcogenide glass
Chalcogenide glass (pronounced hard ch as in chemistry) is a glass containing one or more heavy chalcogens (sulfur, selenium or tellurium; polonium is also a heavy chalcogen but too radioactive to use). 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 (mainly sulfur-based ones such as As-S or Ge-S) 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 (cooling), they can be switched between an amorphous (glassy) and a crystalline state, thereby changing their optical and electrical properties and allowing the storage of information.
Most stable binary chalcogenide glasses are compounds of a chalcogen and a group 14 or 15 element and may be formed in a wide range of atomic ratios. Ternary glasses are also known.
Not all chalcogenide compositions exist in glassy form, though it is possible to find materials with which these non-glass-forming compositions can be alloyed in order to form a glass. An example of this is gallium sulphide-based glasses. Gallium(III) sulphide on its own is not a known glass former; however, with sodium or lanthanum sulphides it forms a glass, gallium lanthanum sulphide (GLS).
Up until recently, chalcogenide glasses (ChGs) were believed to be predominantly covalently bonded materials and classified as covalent network solids. A most recent and extremely comprehensive university study of more than 265 different ChG elemental compositions, representing 40 different elemental families now shows that the vast majority of chalcogenide glasses are more accurately defined as being predominantly bonded by the weaker van der Waals forces of atomic physics and more accurately classified as van der Waals network solids. They are not exclusively bonded by these weaker vdW forces, and do exhibit varying percentages of covalency, based upon their specific chemical makeup.
Uses include infrared detectors, mouldable infrared optics such as lenses, and infrared optical fibers, with the main advantage being that these materials transmit across a wide range of the infrared electromagnetic spectrum.
The physical properties of chalcogenide glasses (high refractive index, low phonon energy, high nonlinearity) also make them ideal for incorporation into lasers, planar optics, photonic integrated circuits, and other active devices especially if doped with rare-earth element ions. Some chalcogenide glasses exhibit several non-linear optical effects such as photon-induced refraction, and electron-induced permittivity modification