Bismuth telluride

Bismuth telluride

Identifiers
CAS Number	1304-82-1 Y
3D model (Jmol)	Interactive image
ChemSpider	11278988 Y
ECHA InfoCard	100.013.760
EC Number	215-135-2
PubChem	6379155
InChI InChI=1S/2Bi.3Te/q2*+3;3*-2 Y Key: AZFMNKUWQAGOBM-UHFFFAOYSA-N Y InChI=1/2Bi.3Te/q2*+3;3*-2 Key: AZFMNKUWQAGOBM-UHFFFAOYAF
SMILES [Te-2].[Te-2].[Te-2].[Bi+3].[Bi+3]
Properties
Chemical formula	Bi2Te3
Molar mass	800.761 g/mol
Appearance	grey powder
Density	7.85 g/cm3
Melting point	586 °C (1,087 °F; 859 K)
Solubility in water	insoluble
Solubility	insoluble
Structure
Crystal structure	Trigonal, hR15, SpaceGroup = R-3m, No. 166
Hazards
Safety data sheet	Sigma-Aldrich
NFPA 704	0 2 0
Flash point	noncombustible
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp) (pure) none (doped with selenium sulfide)
REL (Recommended)	TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp) (pure) TWA 5 mg/m3 (doped with selenium sulfide)
IDLH (Immediate danger)	N.D. (pure and doped)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
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. Bi₂Te₃ is also known to be a topological insulator, and thus exhibits many thickness-dependent physical 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. Bi₂Te₃ cleaves easily along the trigonal axis due to Van der Waals bonding between neighboring tellurium atoms. Due to this, bismuth telluride based materials 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.

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, 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.

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.