Different types of superconductors
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 agreement with conventional models.
This criterion is useful as BCS theory has successfully explained the properties of conventional superconductors since 1957, yet there have been no satisfactory theories to fully explain unconventional superconductors. In most cases conventional superconductors are type I, but there are exceptions such as niobium, which is both conventional and type II.
By their critical temperature.
77 K is used as the demarcation point to emphasize whether or not superconductivity in the materials can be achieved 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).
Most superconductors made of pure elements are type I (except niobium, technetium, vanadium, silicon, and the above-mentioned carbon allotropes).
See also.
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References.
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