Chemistry:Bismuth antimonide

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Bismuth antimonide
Identifiers
3D model (JSmol)
ChemSpider
Properties
BiSb
Molar mass 330.74 g/mol
Appearance Faint-grey to dark-grey powder
Density 8.31 g/cm3
Solubility insoluble
Structure
Hexagonal, A7, SpaceGroup = R-3m, No. 166
a = 4.546A, c = 11.860A[1]
Hazards
Safety data sheet [1]
GHS pictograms GHS07: HarmfulGHS09: Environmental hazard
GHS Signal word Warning
H302, H332, H411
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
2
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

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

Some, in particular Bi0.9Sb0.1, were the first experimentally-observed three-dimensional topological insulators, materials that have conducting surface states but have an insulating interior.[2]

Various BiSb alloys also superconduct at low temperatures,[3] are semiconductors,[1] and are used in thermoelectric devices.[4]

Bismuth antimonide itself (see box to right) is sometimes described as Bi2Sb2.[5]

Synthesis

Crystals of bismuth antimonides are synthesized by melting bismuth and antimony together under inert gas or vacuum. Zone melting is used to decrease the concentration of impurities.[4] When synthesizing single crystals of bismuth antimonides, it is important that impurities are removed from the samples, as oxidation occurring at the impurities leads to polycrystalline growth.[1]

Properties

Topological insulator

Pure bismuth is a semimetal, containing a small band gap, which leads to it having a relatively high conductivity (7.7×105 S/m at 20 °C). When the bismuth is doped with antimony, the conduction band decreases in energy and the valence band increases in energy. At an antimony concentration of 4%, the two bands intersect, forming a Dirac point[2] (which is defined as a point where the conduction and valence bands intersect). Further increases in the concentration of antimony result in a band inversion, in which the energy of the valence band becomes greater than that of the conduction band at specific momenta. Between Sb concentrations of 7 and 22%, the bands no longer intersect, and the Bi1−xSbx becomes an inverted-band insulator.[6] It is at these higher concentrations of Sb that the band gap in the surface states vanishes, and the material thus conducts at its surface.[2]

Superconductor

The highest temperatures at which Bi0.4Sb0.6, as a thin film of thicknesses 150–1350 Å, superconducts (the critical temperature Tc) is approximately 2 K.[3] Single crystal Bi0.935Sb0.065 can superconduct at slightly higher temperatures, and at 4.2 K, its critical magnetic field Bc (the maximum magnetic field that the superconductor can expel) of 1.6 T at 4.2 K.[7]

Semiconductor

Electron mobility is one important parameter describing semiconductors because it describes the rate at which electrons can travel through the semiconductor. At 40 K, electron mobility ranged from 4.9×105 cm2/V·s at an antimony concentration of 0 to 2.4×105 cm2/V·s at an antimony concentration of 7.2%.[1] This is much greater than the electron mobility of other common semiconductors like silicon, which is 1400 cm2/V·s at room temperature.[8]

Another important parameter of Bi1−xSbx is the effective electron mass (EEM), a measure of the ratio of the acceleration of an electron to the force applied to an electron. The effective electron mass is 2×10−3 me for x = 0.11 and 9×10−4 me at x = 0.06.[2] This is much less than the electron effective mass in many common semiconductors (1.09 in Si at 300 K, 0.55 in Ge, and 0.067 in GaAs). A low EEM is good for Thermophotovoltaic applications.

Thermoelectric

Bismuth antimonides are used as the n-type legs in many thermoelectric devices below room temperature. The thermoelectric efficiency, given by its figure of merit zT = σS2T/λ, where S is the Seebeck coefficient, λ is the thermal conductivity, and σ is the electrical conductivity, describes the ratio of the energy provided by the thermoelectric to the heat absorbed by the device. At 80 K, the figure of merit (zT) for Bi1−xSbx peaks at 6.5×10−3 K−1 when x = 0.15.[4] Also, the Seebeck coefficient (the ratio of the potential difference between ends of a material to the temperature difference between the sides) at 80 K of Bi0.9Sb0.1 is −140 μV/K, much lower than the Seebeck coefficient of pure bismuth, −50 μV/K.[9]

References

  1. ↑ 1.0 1.1 1.2 1.3 Jain, A. L. (1959). "Temperature Dependence of the Electrical Properties of Bismuth-Antimony Alloys". Physical Review 114 (6): 1518–1528. doi:10.1103/physrev.114.1518. Bibcode: 1959PhRv..114.1518J. 
  2. ↑ 2.0 2.1 2.2 2.3 Hsieh, D.; Qian, D.; Wray, L.; Xia, Y.; Hor, Y. S.; Cava, R. J.; Hasan, M. Z. (2008-04-24). "A topological Dirac insulator in a quantum spin Hall phase". Nature 452 (7190): 970–974. doi:10.1038/nature06843. ISSN 0028-0836. PMID 18432240. Bibcode: 2008Natur.452..970H. http://www.nature.com/nature/journal/v452/n7190/full/nature06843.html. 
  3. ↑ 3.0 3.1 Zally, G. D.; Mochel, J. M. (1971). "Fluctuation Heat Capacity in Superconducting Thin Films of Amorphous BiSb". Physical Review Letters 27 (25): 1710–1712. doi:10.1103/physrevlett.27.1710. Bibcode: 1971PhRvL..27.1710Z. 
  4. ↑ 4.0 4.1 4.2 Smith, G. E.; Wolfe, R. (1962-03-01). "Thermoelectric Properties of Bismuth‐Antimony Alloys". Journal of Applied Physics 33 (3): 841–846. doi:10.1063/1.1777178. ISSN 0021-8979. Bibcode: 1962JAP....33..841S. 
  5. ↑ PubChem. "Bismuth, compd. with antimony (1:1)" (in en). https://pubchem.ncbi.nlm.nih.gov/compound/6914523. 
  6. ↑ Shuichi Murakami (2007). "Phase transition between the quantum spin Hall and insulator phases in 3D: emergence of a topological gapless phase". New Journal of Physics 9 (9): 356. doi:10.1088/1367-2630/9/9/356. Bibcode: 2007NJPh....9..356M. 
  7. ↑ Kasumov, A. Yu.; Kononenko, O. V.; Matveev, V. N.; Borsenko, T. B.; Tulin, V. A.; Vdovin, E. E.; Khodos, I. I. (1996). "Anomalous Proximity Effect in the Nb–BiSb–Nb Junctions". Physical Review Letters 77 (14): 3029–3032. doi:10.1103/physrevlett.77.3029. PMID 10062113. Bibcode: 1996PhRvL..77.3029K. 
  8. ↑ "Electrical properties of Silicon (Si)". http://www.ioffe.rssi.ru/SVA/NSM/Semicond/Si/electric.html. 
  9. ↑ Goldsmid, H. J. (1970-01-16). "Bismuth–antimony alloys". Physica Status Solidi A 1 (1): 7–28. doi:10.1002/pssa.19700010102. ISSN 1521-396X. Bibcode: 1970PSSAR...1....7G. 



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