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Line 1: − + − Type II superconductors are usually metal oxide alloys or complex oxide ceramics. They can have significantly higher critical temperatures than type I super conductors, with the highest recorded temperature of a type II superconductor being 138K. As yet these is no widely accepted theory to describe the microscopic behaviour of type II superconductors. + + +
not all type II superconductors are oxides
'''Superconductivity''' is a property exhibited by some materials at very low temperatures. It was discovered by Kamerlingh Onnes in 1911. Superconductivity is characterized by two phenomena. First, the disappearance of all electrical [[resistance]] below a certain temperature (known as the critical temperature). Second, the exclusion of any magnetic fields from the bulk of the material below the same temperature. This second property is known as the "Meissner Effect".
'''Superconductivity''' is a property exhibited by some materials at very low temperatures. It was discovered by Kamerlingh Onnes in 1911. Superconductivity is characterized by two phenomena. First, the disappearance of all electrical [[resistance]] below a certain temperature (known as the critical temperature). Second, the exclusion of any magnetic fields from the bulk of the material below the same temperature. This second property is known as the "Meissner Effect".
There are two types of superconductors. Type I superconductors are usually pure metals or alloys. Lead (critical temperature 7.2K) and aluminium (critical temperature 1.2K) are both type I superconductors. A microscopic theory explaining the behaviour of type I superconductors was developed by Bardeen, Cooper and Schrieffer.
There are two types of superconductors. Type I superconductors are usually pure metals or alloys. They are characterized by having a single critical magnetic field, above which the superconductivity is destroyed. Lead (critical temperature T<sub>c</sub> 7.2K) and aluminium (critical temperature 1.2K) are both type I superconductors. A microscopic theory explaining the behaviour of type I superconductors was developed by Bardeen, Cooper and Schrieffer.
A type II superconductor have both an upper (Hc2) and lower (Hc1) critical field. When the applied magnetic field (H) is less than Hc1, the field is excluded, as with a type I superconductor. When H>Hc2, superconductivity is destroyed. Between these limits, the field penetrates the bulk of the superconductor along thin lines of "normal" (non-superconducting) regions. Type II superconductors can operate under significantly higher magnetic fields; they are used commercially to make strong magnets. Examples of type II superconductors include Nb<sub>3</sub>Sn (T<sub>c</sub>=18K) and the high-temperature copper-oxide materials such as YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (T<sub>c</sub>=90K).
The oxide superconductors represent a new class of materials, with critical temperatures as high as 138K. As yet these is no widely accepted theory to describe the microscopic behaviour of these superconductors.
[[category:physics]]
[[category:physics]]