Tellurides, are compounds derived from the telluride anion, Te2-. As tellurium is a member of group 16 on the periodic table, it is considered a chalcogen, and telluride compounds belong to a class of compounds known as chalcogenides.
Alkali metal and alkaline earth chalcogenides are typically colorless, water-soluble compounds used primarily as reagents in chemical synthesis. In contrast, transition metal chalcogenides exhibit a more covalent bond character and useful electronic and optical properties, and many are brightly colored. These are the chalcogenides most often used directly as functional materials; they are found as pigments, catalysts, optical materials, phase change materials, solid electrolytes, or semiconductors. The properties of main-group chalcogenides are less generalizable, but like transition metal halides, they exhibit covalent bonding and many have direct applications. Many chalcogenides compounds occur naturally as minerals such as pyrite (iron sulfide) and calaverite (gold telluride).
Notable tellurides include the II-VI compounds zinc telluride, cadmium telluride, and mercury telluride, semiconductors notable for their use in optoelectronic devices. These materials are direct-bandgap binary semiconductors, and can be alloyed to produce ternary compounds with bandgaps tunable by adjusting precise elemental composition. Of these, cadmium telluride deserves special mention, as it is the basis for cadmium telluride (CdTe) photovoltaics, currently the primary non-silicon-based solar cell technology being employed on a grand scale. Additionally, bismuth telluride and lead telluride are semiconductor materials that exhibit the thermoelectric effect, lending them to use in thermoelectric generators, specialized cooling devices, and thermocouples. Recently, many of these telluride compounds have been shown to act as topological insulators--the bulk of the material behaves as an insulator, while the surfaces and edges behave as conductors. This unique property is being intensely studied, and may eventually be exploited to improve the functioning of practical electronic devices such as computers.