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Bismuth antimonide
Identifiers
CAS Number	12323-19-2;
3D model (JSmol)	Interactive image;
ChemSpider	11201349;
ECHA InfoCard	100.204.020
PubChem CID	69145232.1.1InChI;
	InChI InChI=1S/2Bi.2Sb; Key: AEMQIQQWIVNHAU-UHFFFAOYSA-N;
	SMILES [Sb].[Sb].[Bi].[Bi];
Properties
Chemical formula	BiSb
Molar mass	330.74 g/mol
Appearance	Faint-grey to dark-grey powder
Density	8.31 g/cm3
Solubility	insoluble
Structure
Crystal structure	Hexagonal, A7, SpaceGroup = R-3m, No. 166
Lattice constant	a = 4.546A, c = 11.860A
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H332, H411
NFPA 704 (fire diamond)	2 0 0
Safety data sheet (SDS)	[1]
	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, (Bi_1−xSb_x) are binary alloys of bismuth and antimony in various ratios.

Some, in particular Bi_0.9Sb_0.1, 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 Bi_1−xSb_x 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 Bi_0.4Sb_0.6, as a thin film of thicknesses 150–1350 Å, superconducts (the critical temperature T_c) is approximately 2 K.^[3] Single crystal Bi_0.935Sb_0.065 can superconduct at slightly higher temperatures, and at 4.2 K, its critical magnetic field B_c (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 Bi_1−xSb_x 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 m_e for x = 0.11 and 9×10⁻⁴ m_e 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 z_T = ⁠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 (z_T) for Bi_1−xSb_x 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 Bi_0.9Sb_0.1 is −140 μV/K, much lower than the Seebeck coefficient of pure bismuth, −50 μV/K.^[9]

References

^ ^a ^b ^c ^d 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.
^ ^a ^b ^c ^d 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.
^ ^a ^b 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.
^ ^a ^b ^c 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.
^ PubChem. "Bismuth, compd. with antimony (1:1)". pubchem.ncbi.nlm.nih.gov. Retrieved 2021-06-15.
^ 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.
^ 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.
^ "Electrical properties of Silicon (Si)". www.ioffe.rssi.ru. Retrieved 2015-12-11.
^ 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.