Bismuth telluride

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Bismuth telluride
Monokristall tellurida vismuta.jpg
Single crystal of bismuth telluride
Bi2Te3 structure 2.png
Atomic structure: ideal (l) and with a twin defect (r)
Twin in Bi2Te3 3.jpg
Electron micrograph of twinned bismuth telluride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.760 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 215-135-2
PubChem CID
UNII
  • InChI=1S/2Bi.3Te/q2*+3;3*-2 Yes check.svgY
    Key: AZFMNKUWQAGOBM-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/2Bi.3Te/q2*+3;3*-2
    Key: AZFMNKUWQAGOBM-UHFFFAOYAF
  • [Te-2].[Te-2].[Te-2].[Bi+3].[Bi+3]
Properties
Bi2Te3
Molar mass 800.76 g·mol−1
AppearanceGrey powder or metallic grey crystals
Density 7.74 g/cm3 [1]
Melting point 580 °C (1,076 °F; 853 K) [1]
insoluble [1]
Solubility in ethanol soluble [1]
Structure
Trigonal, hR15
R3m, No. 166 [2]
a = 0.4395 nm, c = 3.044 nm
3
Hazards
NFPA 704 (fire diamond)
NFPA 704.svgHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
0
0
Flash point noncombustible [3]
NIOSH (US health exposure limits):
PEL (Permissible)
TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp) (pure)
none (doped with selenium sulfide) [3]
REL (Recommended)
TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp) (pure) TWA 5 mg/m3 (doped with selenium sulfide) [3]
IDLH (Immediate danger)
N.D. (pure and doped) [3]
Safety data sheet (SDS) Sigma-Aldrich
Related compounds
Other anions
Other cations
Arsenic telluride
Antimony telluride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

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 a topological insulator, and thus exhibits thickness-dependent physical properties.

Contents

Properties as a thermoelectric material

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. [4] 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. [5]

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 °C, [6] 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. [7]

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. [8]

Properties as a topological insulator

Bismuth telluride is a well-studied topological insulator. Its physical properties have been shown to change at highly reduced thicknesses, when its conducting surface states are exposed and isolated. These thin samples are obtained through either epitaxy or mechanical exfoliation.

Epitaxial growth methods such as molecular beam epitaxy and metal organic chemical vapor deposition are common methods of obtaining thin Bi2Te3 samples. The stoichiometry of samples obtained through such techniques can vary greatly between experiments, so Raman spectroscopy is often used to determine relative purity. However, thin Bi2Te3 samples are resistant to Raman spectroscopy due to their low melting point and poor heat dispersion. [9]

The crystalline structure of Bi2Te3 allows for mechanical exfoliation of thin samples by cleaving along the trigonal axis. This process is significantly lower in yield than epitaxial growth, but produces samples without defects or impurities. Similar to extracting graphene from bulk graphite samples, this is done by applying and removing adhesive tape from successively thinner samples. This procedure has been used to obtain Bi2Te3 flakes with a thickness of 1 nm. [10] However, this process can leave significant amounts of adhesive residue on a standard Si/SiO2 substrate, which in turn obscure atomic force microscopy measurements and inhibit the placement of contacts on the substrate for purposes of testing. Common cleaning techniques such as oxygen plasma, boiling acetone and isopropyl alcohol are ineffective in removing residue. [11]

Occurrence and preparation

The mineral form of Bi2Te3 is tellurobismuthite which is moderately rare. [12] [13] There are many natural bismuth tellurides of different stoichiometry, as well as compounds of the Bi-Te-S-(Se) system, like Bi2Te2S (tetradymite). These bismuth tellurides are part of the tetradymite group of minerals. [14]

Bismuth telluride may be prepared simply by sealing mixed powders 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

Related Research Articles

<span class="mw-page-title-main">Tellurium</span> Chemical element with atomic number 52 (Te)

Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally found in its native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is due partly to its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth.

<span class="mw-page-title-main">Thermoelectric cooling</span> Electrically powered heat-transfer

Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC) and occasionally a thermoelectric battery. It can be used either for heating or for cooling, although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.

<span class="mw-page-title-main">Thermoelectric materials</span> Materials whose temperature variance leads to voltage change

Thermoelectric materials show the thermoelectric effect in a strong or convenient form.

<span class="mw-page-title-main">Seebeck coefficient</span> Measure of voltage induced by change of temperature

The Seebeck coefficient of a material is a measure of the magnitude of an induced thermoelectric voltage in response to a temperature difference across that material, as induced by the Seebeck effect. The SI unit of the Seebeck coefficient is volts per kelvin (V/K), although it is more often given in microvolts per kelvin (μV/K).

<span class="mw-page-title-main">Semimetal</span> Metal with a small negative indirect band-gap

A semimetal is a material with a small energy overlap between the bottom of the conduction band and the top of the valence band, but they do not overlap in momentum space. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger than that of a semiconductor. Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a small density of states at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.

<span class="mw-page-title-main">Tetradymite</span>

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. Traces of selenium are usually present.

<span class="mw-page-title-main">Tellurobismuthite</span>

Tellurobismuthite, or tellurbismuth, is a telluride mineral: bismuth telluride (Bi2Te3). It crystallizes in the trigonal system. There are natural cleavage planes in the (0001) direction as the crystal is effectively lamellar (layered) in that plane. The Mohs hardness is 1.5 – 2 and the specific gravity is 7.815. It is a dull grey color, which exhibits a splendent luster on fresh cleavage planes.

<span class="mw-page-title-main">Lead telluride</span> Chemical compound

Lead telluride is a compound of lead and tellurium (PbTe). It crystallizes in the NaCl crystal structure with Pb atoms occupying the cation and Te forming the anionic lattice. It is a narrow gap semiconductor with a band gap of 0.32 eV. It occurs naturally as the mineral altaite.

<span class="mw-page-title-main">Mercury telluride</span> Topologically insulating chemical compound

Mercury telluride (HgTe) is a binary chemical compound of mercury and tellurium. It is a semi-metal related to the II-VI group of semiconductor materials. Alternative names are mercuric telluride and mercury(II) telluride.

<span class="mw-page-title-main">Thermoelectric generator</span> Device that converts heat flux into electrical energy

A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat directly into electrical energy through a phenomenon called the Seebeck effect. Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient. When the same principle is used in reverse to create a heat gradient from an electric current, it is called a thermoelectric cooler.

<span class="mw-page-title-main">Topological insulator</span> State of matter with insulating bulk but conductive boundary

A topological insulator is a material whose interior behaves as an electrical insulator while its surface behaves as an electrical conductor, meaning that electrons can only move along the surface of the material.

<span class="mw-page-title-main">Antimony telluride</span> Chemical compound

Antimony telluride is an inorganic compound with the chemical formula Sb2Te3. As is true of other pnictogen chalcogenide layered materials, it is a grey crystalline solid with layered structure. Layers consist of two atomic sheets of antimony and three atomic sheets of tellurium and are held together by weak van der Waals forces. Sb2Te3 is a narrow-gap semiconductor with a band gap 0.21 eV; it is also a topological insulator, and thus exhibits thickness-dependent physical properties.

<span class="mw-page-title-main">Alexander A. Balandin</span> American electrical engineer

Alexander A. Balandin is an electrical engineer, solid-state physicist, and materials scientist best known for the experimental discovery of unique thermal properties of graphene and their theoretical explanation; studies of phonons in nanostructures and low-dimensional materials, which led to the development of the field of phonon engineering; investigation of low-frequency electronic noise in materials and devices; and demonstration of the first charge-density-wave quantum devices operating at room temperature.

Bismuth selenide is a gray compound of bismuth and selenium also known as bismuth(III) selenide.

In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds.

Lead tin telluride, also referred to as PbSnTe or Pb1−xSnxTe, is a ternary alloy of lead, tin and tellurium, generally made by alloying either tin into lead telluride or lead into tin telluride. It is a IV-VI narrow band gap semiconductor material.

Bismuth antimonides, Bismuth-antimonys, or Bismuth-antimony alloys, (Bi1−xSbx) are binary alloys of bismuth and antimony in various ratios.

<span class="mw-page-title-main">Dirac cone</span> Quantum effect in some non-metals

In physics, Dirac cones are features that occur in some electronic band structures that describe unusual electron transport properties of materials like graphene and topological insulators. In these materials, at energies near the Fermi level, the valence band and conduction band take the shape of the upper and lower halves of a conical surface, meeting at what are called Dirac points.

<span class="mw-page-title-main">Boron nitride nanosheet</span>

Boron nitride nanosheet is a crystalline form of the hexagonal boron nitride (h-BN), which has a thickness of one atom. Similar in geometry as well as physical and thermal properties to its carbon analog graphene, but has very different chemical and electronic properties – contrary to the black and highly conducting graphene, BN nanosheets are electrical insulators with a band gap of ~5.9 eV, and therefore appear white in color.

<span class="mw-page-title-main">Joseph P. Heremans</span> Condensed matter experimental physicist

Joseph P. Heremans is a condensed matter experimental physicist at The Ohio State University where he holds titles as Ohio Eminent Scholar and Professor in the Department of Mechanical and Aerospace Engineering, with courtesy appointments in the Department of Physics and Department of Materials Science and Engineering. He is a member of the National Academy of Engineering and fellow of the American Physical Society and the American Association for the Advancement of Science. His research focuses on magneto-transport, thermal, and thermoelectric properties of electrons, phonons, and spin in narrow-gap semiconductors, semimetals, and nanostructures. Prior to OSU, Heremans worked as a research scientist and research manager at GM Research Lab from 1984-1998 and the Delphi Research Labs (1999-2005), where he developed tunable IR diode lasers and magnetic sensors.

References

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