Bismuth telluride, doped with

Bismuth telluride, doped with Selenium sulfide (as Bi2Te3)... 

The results of animal experiments have shown that bismuth interferes with copper and zinc metabolism but do not suggest that bismuth is carcinogenic. Industrial air standards exist only for bismuth telluride and bismuth telluride doped with selenium, for which the Occupational Safety and Health Administration (OSHA) and ACGIH TLVs are 5 mg/m. ... 

Synonyms/Trade Names Doped bismuth sesquitelluride. Doped bismuth telluride. Doped bismuth tritelluride. Doped tellurobismuthite [Note Doped with selenium sulfide. Commercial mix may contain 80% Bi2Tej, 20% stannous telluride, plus some tellurium ] ... 

Calvet and Guillaud (S3) noted in 1965 that in order to increase the sensitivity of a heat-flow microcalorimeter, thermoelectric elements with a high factor of merit must be used. (The factor of merit / is defined by the relation / = e2/pc, where e is the thermoelectric power of the element, p its electrical resistivity, and c its thermal conductivity.) They remarked that the factor of merit of thermoelements constructed with semiconductors (doped bismuth tellurides usually) is approximately 19 times greater than the factor of merit of chromel-to-constantan thermocouples. They described a Calvet-type microcalorimeter in which 195 semiconducting thermoelements were used instead of the usual thermoelectric pile. 

Toxicology. Bismuth telluride, either alone or doped with selenium sulfide, is apparently of very low toxicity. 

Seebeck experimented with a number of metals including antimony, iron, zinc, silver, gold, lead, mercury, copper, platinum, and bismuth. Later, the observation was made that the electromotive force (EMF) generated is proportional to the temperature difference between the junctions. Today, TE couples are often made from semiconductor alloys of bismuth antimony telluride, Bi Sb2- cTe3 (x 0.5), that have been suitably doped to possess distinct n- or p-type characteristics. A practical TE cooler consists of one or more couples that are connected electrically in series and thermally in parallel. 

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