Title: Bismuth Telluride
CAS Registry Number: 1304-82-1
Additional Names: Tellurobismuthite
Molecular Formula: Bi2Te3
Molecular Weight: 800.76
Percent Composition: Bi 52.20%, Te 47.80%
Literature References: Prepd by heating stoichiometric amounts of the elements to 475° for several days in an evacuated glass or quartz tube: Dönges, Z. Anorg. Allg. Chem. 265, 56 (1951). Prepn of single crystals: Ainsworth, Proc. Phys. Soc. London B69, 606 (1956); in zone-melting apparatus: Harmon et al., J. Phys. Chem. Solids 2, 181 (1957). Review of different methods: Minden, Sylvania Technol. 11 (no. 1), 13-25 (1958).
Properties: Gray hexagonal platelets. d 7.642. mp 585°. Single crystals have been grown by the Czochralski technique in which a hydrogen atmosphere was used to minimize the evaporation of tellurium. Since the crystals cleave readily along the (0001) basal hexagonal plane, it is mechanically easier to orient the seed so that the growth direction is in this plane rather than normal to it. The resulting crystals grow more readily along the basal plane, so that they have an oval cross section, often with a characteristic notch. All crystals so pulled are the P type. Heat of formation: -8 kcal/mol. Resistivity: 0.00033 ohm-cm. Thermal conductivities at room temp: l0 = 0.015 watt/cm-deg; le = 1.4 ´ 10-3 watt/cm-deg. Energy gap: 0.15 ev. Electron mobility: 800 cm2/volt-sec. Hole mobility: 400 cm2/volt-sec.
Melting point: mp 585°
Density: d 7.642
CAUTION: Potential symptoms of overexposure are irritation of eyes, skin, upper respiratory system; garlic breath. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 28.
Use: In electronics as semiconductor.