Bismuth telluride
Encyclopedia
Bismuth telluride 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.
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/(m2·K), similar to ordinary glass
.
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
).
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
and tellurium also known as bismuth(III) telluride. It is a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
which, when alloyed with antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
or selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...
is an efficient thermoelectric material for refrigeration or portable power generation. Topologically protected surface states
Topological insulator
A topological insulator is a material that behaves as an insulator in its interior or bulk while permitting the movement of charges on its surface....
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. 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
N-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
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
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
of 1.20 W/(m2·K), similar to ordinary glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
.
Occurrence
The mineralMineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
form of Bi2Te3 is tellurobismuthite
Tellurobismuthite
Tellurobismuthite is a telluride mineral: bismuth telluride . It has a trigonal structure and lattice parameters a=0.439 nm and c=3.06 nm. There are natural cleavage planes in the direction as the crystal is effectively lamellar in that plane. The Mohs hardness is 2 and the specific gravity is...
which is moderately rare. There are many natural bismuth tellurides of different stoichiometry
Stoichiometry
Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers...
, as well as compounds of the Bi-Te-S-(Se) system, like Bi2Te2S (tetradymite
Tetradymite
Tetradymite is a mineral consisting of bismuth, tellurium and sulfide, Bi2Te2S, also known as telluric bismuth. If sulfur is absent the mineral is tellurobismuthite and the formula is then Bi2Te3...
).