Tellurium, discovered in 1782, is a rare metalloid with density 6.24 g/cm³ and melting point 450 °C, occurring only as a trace byproduct in copper and gold ores. It is used in tiny amounts, yet changes material performance in steel, alloys and new-energy materials. In metallurgy, a small tellurium addition to low-carbon and free-machining steel improves machinability by making chips break cleanly and extending tool life; adding it to copper alloys raises conductivity and corrosion resistance for cable lugs and electrical terminals. The largest emerging use is cadmium telluride (CdTe) thin-film solar cells, where a near-micron-thick CdTe absorber layer converts sunlight at low cost with good weak-light performance, making CdTe one of the few thin-film PV routes commercialized at scale. Phase-change memory exploits the rapid resistance switching of tellurium-based alloys between crystalline and amorphous states, serving as high-speed storage media in solid-state drives and being explored for neuromorphic chips. Tellurium is also used as a rubber vulcanizer, ceramic colorant and infrared optical element.
Cadmium telluride (CdTe) is tellurium's most industrially meaningful compound, forming the absorber layer of thin-film solar cells: with a direct bandgap and extremely high absorption coefficient, a few microns absorb most visible light, letting modules stay thin, perform well in weak light, and reach commercial deployment in utility-scale PV plants. Tellurium dioxide (TeO2) is a white crystal valued for its strong acousto-optic effect, used in acousto-optic modulators, deflectors and infrared windows for lasers and fiber-optic telecom. Bismuth telluride (Bi2Te3) is the classic room-temperature thermoelectric material, combining low lattice thermal conductivity with a high Seebeck coefficient; it powers portable thermoelectric coolers, localized CPU cooling and miniature waste-heat modules, and is a familiar semiconductor in consumer electronics. Zinc telluride (ZnTe) is used for infrared windows and LED doping. Sodium tellurite (Na2TeO3) is a minor additive in electroplating baths and microbiological media.
