Bismuth telluride

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Bismuth telluride
Identifiers
CAS number 1304-82-1 YesY
PubChem 6379155
ChemSpider 11278988 YesY
EC number 215-135-2
Jmol-3D images {{#if:[Te-2].[Te-2].[Te-2].[Bi+3].[Bi+3]|Image 1
Properties
Molecular formula Bi2Te3
Molar mass 800.761 g/mol
Appearance grey powder
Density 7.642 g/cm3
Melting point 585 °C; 1,085 °F; 858 K ([1])
Solubility in water insoluble
Solubility soluble in ethanol
Structure
Crystal structure Trigonal, hR15, SpaceGroup = R-3m, No. 166
Hazards
NFPA 704
0
2
0
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Bismuth telluride (Bi2Te3) is a gray powder that is a compound of bismuth and tellurium also known as bismuth(III) telluride. It is a semiconductor which, when alloyed with antimony or selenium is an efficient thermoelectric material for refrigeration or portable power generation. Topologically protected surface states have been observed in bismuth telluride.

Thermoelectric properties

Bismuth telluride is a narrow gap layered semiconductor with a trigonal unit cell. The valence and conduction band structure can be described as a many-ellipsoidal model with 6 constant-energy ellipsoids that are centered on the reflection planes.[2] Bi2Te3 cleaves easily along the trigonal axis due to Van der Waals bonding between neighboring tellurium atoms. Due to this, bismuth telluride based material that are used for power generation or cooling applications must be polycrystalline. Furthermore, the Seebeck coefficient of bulk Bi2Te3 becomes compensated around room temperature, forcing the materials used in power generation devices to be an alloy of bismuth, antimony, tellurium, and selenium.[1]

Recently, researchers have attempted to improve the efficiency of Bi2Te3 based materials by creating structures where one or more dimensions are reduced, such as nanowires or thin films. In one such instance n-type bismuth telluride was shown to have an improved Seebeck coefficient (voltage per unit temperature difference) of −287 μV/K at 54 Celsius,[3] However, one must realize that Seebeck Coefficient and electrical conductivity have a tradeoff; a higher Seebeck coefficient results in decreased carrier concentration and decreased electrical conductivity.[4]

In another case, researchers report that bismuth telluride has high electrical conductivity of 1.1×105 S·m/m2 with its very low lattice thermal conductivity of 1.20 W/(m·K), similar to ordinary glass.[5]

Occurrence

A scanning electron microscopy image of small crystals of bismuth telluride, in the same form as tellurobismuthite
The mineral form of Bi2Te3 is tellurobismuthite which is moderately rare. There are many natural bismuth tellurides of different stoichiometry, as well as compounds of the Bi-Te-S-(Se) system, like Bi2Te2S (tetradymite).

Preparation

Bismuth Telluride is prepared by sealing a sample of bismuth and tellurium metal in a quartz tube under vacuum (critical, as an unsealed or leaking sample may explode in a furnace) and heating it to 800°C in a muffle furnace.

See also

References

  1. ↑ 1.0 1.1 Satterthwaite, C. B.; Ure, R. (1957). "Electrical and Thermal Properties of Bi2Te3". Phys. Rev. 108 (5): 1164. doi:10.1103/PhysRev.108.1164. 
  2. ↑ Caywood, L. P.; Miller, G. (1970). "Anisotropy of the constant energy surfaces in p-type Bi2Te3 and Bi2Se3 from galvanomagnetic coefficients". Phys. Rev. B. 2 (8): 3209. doi:10.1103/PhysRevB.2.3209. 
  3. ↑ Tan, J. (2005). "Thermoelectric properties of bismuth telluride thin films deposited by radio frequency magnetron sputtering". Proceedings of SPIE 5836. p. 711. doi:10.1117/12.609819. 
  4. ↑ H. J. Goldsmid, A. R. Sheard, and D. A. Wright (1958). "The performance of bismuth telluride thermojunctions". Br. J. Appl. Phys. 9 (9): 365. doi:10.1088/0508-3443/9/9/306. 
  5. ↑ M. Takeiishi et a'.. "Thermal conductivity measurements of Bismuth Telluride thin films by using the 3 Omega method". The 27th Japan Symposium on Thermophysical Properties, 2006, Kyoto. Archived from the original on 2007-06-28. Retrieved 2009-06-06. 

External links

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