There is no uniform standard for the classification of superconductors
There are several types of class methods:
(1) According to the critical temperature at which materials reach superconductivity they can be placed. Divided into high temperature superconductors and low temperature superconductors: leading in strong current applications. The International Electrotechnical Commission (IEC) defines materials above 25 K. It is a high temperature superconductor and a low temperature superconductor below 25 K.
(2) Superconducting materials can be divided into metal superconducting materials according to their chemical composition. Material (can also be divided into elements, alloys, compounds and other superconductors), pottery, ceramic superconducting materials, organic superconducting materials, and semiconductor or insulating superconductors, guide materials and other four categories. Typical metal superconductors include Nb and Pb, NbTi, Nb3Sn, MgB2, etc. Ceramics have copper based oxides, Iron base compounds, etc.; The organic category includes Cs3C60, KxC22H14, etc. SiC, diamond, graphene, etc. belong to the class of insulating superconductors.
(3) According to the difference in the magnetization curve of the superconductor in the magnetic field. There are two types of superconductors. One type of superconductor, called Class I. It's a metal superconductor. It shields the magnetic field, which means magnetic fields cannot enter a superconductor. If the external magnetic field is too strong. It would destroy the superconducting properties of the superconductor. There are only two such superconductors, two states, namely, low temperature superconducting state and normal state. The other is called II. Class superconductors, mainly alloy and ceramic superconductors. For the second. Like superconductors, they have two critical magnetic field values, at both criticals between values (mixed states), the material allows part of the magnetic field to penetrate the material.
Because the second type of superconductor has a higher critical temperature and critical magnetism field can pass through large superconducting currents, so it has higher applications value. Superconducting strong magnetic field made from certain class II superconductors. At present, it has been widely used in superconducting materials.
