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Bismuth antimonide
Chemical compound

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.

Various BiSb alloys also superconduct at low temperatures, are semiconductors, and are used in thermoelectric devices.

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

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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.6 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.7

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 point8 (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.9 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.10

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.11 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.12

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%.13 This is much greater than the electron mobility of other common semiconductors like silicon, which is 1400 cm2/V·s at room temperature.14

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 = 0.06.15 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 = 0.15.16 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.17

References

  1. 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. arXiv:0902.1356. Bibcode:2008Natur.452..970H. doi:10.1038/nature06843. ISSN 0028-0836. PMID 18432240. S2CID 4402113. http://www.nature.com/nature/journal/v452/n7190/full/nature06843.html ↩

  2. Zally, G. D.; Mochel, J. M. (1971). "Fluctuation Heat Capacity in Superconducting Thin Films of Amorphous BiSb". Physical Review Letters. 27 (25): 1710–1712. Bibcode:1971PhRvL..27.1710Z. doi:10.1103/physrevlett.27.1710. /wiki/Bibcode_(identifier) ↩

  3. Jain, A. L. (1959). "Temperature Dependence of the Electrical Properties of Bismuth-Antimony Alloys". Physical Review. 114 (6): 1518–1528. Bibcode:1959PhRv..114.1518J. doi:10.1103/physrev.114.1518. /wiki/Bibcode_(identifier) ↩

  4. Smith, G. E.; Wolfe, R. (1962-03-01). "Thermoelectric Properties of Bismuth-Antimony Alloys". Journal of Applied Physics. 33 (3): 841–846. Bibcode:1962JAP....33..841S. doi:10.1063/1.1777178. ISSN 0021-8979. /wiki/Bibcode_(identifier) ↩

  5. PubChem. "Bismuth, compd. with antimony (1:1)". pubchem.ncbi.nlm.nih.gov. Retrieved 2021-06-15. https://pubchem.ncbi.nlm.nih.gov/compound/6914523 ↩

  6. Smith, G. E.; Wolfe, R. (1962-03-01). "Thermoelectric Properties of Bismuth-Antimony Alloys". Journal of Applied Physics. 33 (3): 841–846. Bibcode:1962JAP....33..841S. doi:10.1063/1.1777178. ISSN 0021-8979. /wiki/Bibcode_(identifier) ↩

  7. Jain, A. L. (1959). "Temperature Dependence of the Electrical Properties of Bismuth-Antimony Alloys". Physical Review. 114 (6): 1518–1528. Bibcode:1959PhRv..114.1518J. doi:10.1103/physrev.114.1518. /wiki/Bibcode_(identifier) ↩

  8. 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. arXiv:0902.1356. Bibcode:2008Natur.452..970H. doi:10.1038/nature06843. ISSN 0028-0836. PMID 18432240. S2CID 4402113. http://www.nature.com/nature/journal/v452/n7190/full/nature06843.html ↩

  9. 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. arXiv:0710.0930. Bibcode:2007NJPh....9..356M. doi:10.1088/1367-2630/9/9/356. S2CID 13999448. /wiki/ArXiv_(identifier) ↩

  10. 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. arXiv:0902.1356. Bibcode:2008Natur.452..970H. doi:10.1038/nature06843. ISSN 0028-0836. PMID 18432240. S2CID 4402113. http://www.nature.com/nature/journal/v452/n7190/full/nature06843.html ↩

  11. Zally, G. D.; Mochel, J. M. (1971). "Fluctuation Heat Capacity in Superconducting Thin Films of Amorphous BiSb". Physical Review Letters. 27 (25): 1710–1712. Bibcode:1971PhRvL..27.1710Z. doi:10.1103/physrevlett.27.1710. /wiki/Bibcode_(identifier) ↩

  12. 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. Bibcode:1996PhRvL..77.3029K. doi:10.1103/physrevlett.77.3029. PMID 10062113. /wiki/Bibcode_(identifier) ↩

  13. Jain, A. L. (1959). "Temperature Dependence of the Electrical Properties of Bismuth-Antimony Alloys". Physical Review. 114 (6): 1518–1528. Bibcode:1959PhRv..114.1518J. doi:10.1103/physrev.114.1518. /wiki/Bibcode_(identifier) ↩

  14. "Electrical properties of Silicon (Si)". www.ioffe.rssi.ru. Retrieved 2015-12-11. http://www.ioffe.rssi.ru/SVA/NSM/Semicond/Si/electric.html ↩

  15. 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. arXiv:0902.1356. Bibcode:2008Natur.452..970H. doi:10.1038/nature06843. ISSN 0028-0836. PMID 18432240. S2CID 4402113. http://www.nature.com/nature/journal/v452/n7190/full/nature06843.html ↩

  16. Smith, G. E.; Wolfe, R. (1962-03-01). "Thermoelectric Properties of Bismuth-Antimony Alloys". Journal of Applied Physics. 33 (3): 841–846. Bibcode:1962JAP....33..841S. doi:10.1063/1.1777178. ISSN 0021-8979. /wiki/Bibcode_(identifier) ↩

  17. Goldsmid, H. J. (1970-01-16). "Bismuth–antimony alloys". Physica Status Solidi A. 1 (1): 7–28. Bibcode:1970PSSAR...1....7G. doi:10.1002/pssa.19700010102. ISSN 1521-396X. /wiki/Bibcode_(identifier) ↩