Superconductor classification
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Superconductors can be classified in accordance with several criteria that depend on physical properties, current understanding, and the expense of cooling them or their material.
By their magnetic properties
- Type I superconductors: those having just one critical field, Hc, and changing abruptly from one state to the other when it is reached.
- Type II superconductors: having two critical fields, Hc1 and Hc2, being a perfect superconductor under the lower critical field (Hc1) and leaving completely the superconducting state to a normal conducting state above the upper critical field (Hc2), being in a mixed state when between the critical fields.
- Type-1.5 superconductor – Multicomponent superconductors characterized by two or more coherence lengths
By the understanding we have about them
- Conventional superconductors: those that can be fully explained with the BCS theory or related theories.
- Unconventional superconductors: those that failed to be explained using such theories, e.g.:
This criterion is important, as the BCS theory has explained the properties of conventional superconductors since 1957, yet there have been no satisfactory theories to explain unconventional superconductors fully. In most cases, type I superconductors are conventional, but there are several exceptions such as niobium, which is both conventional and type II.
By their critical temperature
- Low-temperature superconductors, or LTS: those whose critical temperature is below 30 K.
- High-temperature superconductors, or HTS: those whose critical temperature is above 30 K.
Some now use 77 K as the split to emphasize whether or not we can cool the sample with liquid nitrogen (whose boiling point is 77K), which is much more feasible than liquid helium (an alternative to achieve the temperatures needed to get low-temperature superconductors).
By material constituents and structure
- Some pure elements, such as lead or mercury (but not all pure elements, as some never reach the superconducting phase).
- Some allotropes of carbon, such as fullerenes, nanotubes, or diamond.[citation needed]
- Most superconductors made of pure elements are type I (except niobium, technetium, vanadium, silicon, and the above-mentioned Carbon allotropes)
- Alloys, such as
- Niobium-titanium (NbTi), whose superconducting properties were discovered in 1962.
- Ceramics (often insulators in the normal state), which include
- Cuprates i.e. copper oxides (often layered, not isotropic)
- Iron-based superconductors, including the oxypnictides
- Magnesium diboride (MgB2), whose critical temperature is 39K,[1] being the conventional superconductor with the highest known temperature.
- non-cuprate oxides such as BKBO
- other
- eg the "metallic" compounds Hg
3NbF
6 and Hg
3TaF
6 are both superconductors below 7 K (−266.15 °C; −447.07 °F).[2]
See also
- Conventional superconductor
- covalent superconductors
- List of superconductors
- High-temperature superconductivity
- Room temperature superconductor
- Superconductivity
- Technological applications of superconductivity
- Timeline of low-temperature technology
- Type-I superconductor
- Type-II superconductor
- Unconventional superconductor
References
- ^ Jun Nagamatsu, Norimasa Nakagawa, Takahiro Muranaka, Yuji Zenitani and Jun Akimitsu (March 1, 2001). "Superconductivity at 39 K in magnesium diboride". Nature. 410 (6824): 63–64. Bibcode:2001Natur.410...63N. doi:10.1038/35065039. PMID 11242039.
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: CS1 maint: multiple names: authors list (link) - ^ W.R. Datars, K.R. Morgan and R.J. Gillespie (1983). "Superconductivity of Hg3NbF6 and Hg3TaF6". Phys. Rev. B. 28: 5049–5052. Bibcode:1983PhRvB..28.5049D. doi:10.1103/PhysRevB.28.5049.
- CS1 maint: multiple names: authors list
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