Bismuth-antimony
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PubChem CID
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| 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 | |
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a = 4.546A, c = 11.860A
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| Safety data sheet | [1] |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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.
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. 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.
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 Sb concentration of 4%, the two bands intersect, forming a Dirac point (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. 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.
The highest temperatures at which Bi.4Sb.6 thin film of thicknesses 150-1350A superconduct, the critical temperature Tc, is approximately 2K. Single crystal Bi.935Sb.065 can superconduct at slightly higher temperatures, and at 4.2K, its critical magnetic field Bc (the maximum magnetic field that the superconductor can expel) of 1.6T at 4.2K.
Electron mobility is one important parameter describing semiconductors because it describes the rate at which electrons can travel through the semiconductor. At 40K, electron mobility ranged from 0.49*106 cm2/Vs at an Sb concentration of 0 to .24*106 cm2/Vs at a Sb concentration of 7.2%. This is much greater than the electron mobility of other common semiconductors like Si, which is 1400 cm2/Vs at room temperature.
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