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.

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 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.

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 .

■  General properties
Molar mass Appearance Lattice Parameters Density Melting point Crystal structure
800.761 g/mol Grey pieces a = 4.38 Å,
c = 30.49 Å
7.85 g/cm3 585 °C, hexagonal
 
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