Superconductor, also known as superconducting material, refers to a conductor whose resistance is zero at a certain temperature. In the experiment, if the measured value of the conductor resistance is lower than 10-25Ω, the resistance can be regarded as zero.
Superconductors have been used in a series of experimental applications, and have carried out certain military and commercial applications. They can be used as defect materials for photonic crystals in the field of communications.
Characteristics: Superconductors have three basic characteristics: fully conductive, completely diamagnetic, and flux quantized.
(1) Full electrical conductivity
This is the most basic property of superconducting materials, that is, when the temperature drops below the critical temperature Tc, its resistance becomes zero. The zero resistance characteristics of superconducting materials can be used to transmit power and manufacture large magnets.
(2) Completely diamagnetic
When the superconductor is placed in an external magnetic field, the superconductor will show complete diamagnetism, that is, the magnetic field that is originally in the body will be squeezed out, and the internal magnetic induction intensity is zero. People call this phenomenon the "Meissner effect." Using the complete diamagnetism of superconducting materials, superconducting maglev trains can be manufactured.
(3) Flux quantization
Flux quantization, also known as the Josephson effect, refers to the phenomenon that when an insulating layer between two superconductors is thin to atomic size, electron pairs can pass through the insulating layer to generate a tunneling current, that is, in a superconductor-insulator —Superconductor (superconductor) structure can produce superconducting current.
Classification:
According to the critical temperature of superconducting materials, superconducting materials can be divided into low-temperature superconducting materials and high-temperature superconducting materials. It is generally believed that superconducting materials with Tc <25K are called low-temperature superconducting materials, and currently commercialized include NbTi (Tc = 9.5K) and Nb3Sn (Tc = 18k); superconducting materials with Tc≥25K are called high-temperature superconducting materials Conductive materials, mainly of bismuth series (such as Bi2Sr2Ca2Cu3O7-δ, Tc = 110K), yttrium series (such as YBa2Cu3O7-δ, Tc = 92K) and MgB2 (Tc = 40K) materials are of practical value. Practically valuable bismuth and yttrium high-temperature superconducting materials belong to oxide ceramics.
In the manufacturing process, they must overcome the problems of processing brittleness, precise control of oxygen content, and reaction with the matrix. Therefore, they are expensive and are still in the research and development stage. The low-temperature superconducting materials represented by NbTi and Nb3Sn, due to their excellent mechanical processing performance and cost advantages, will still be in a dominant position in the commercial superconducting market for a long period of time.