Magnesium diboride is an inorganic compound with the chemical formula MgB ₂. Amorphous magnesium diboride is a dark gray, water-insoluble granular solid. In 2001, researchers discovered that magnesium diboride transformed into a superconductor at 39 Kelvin, belonging to the category of conventional superconductors. MgB ₂ is significantly different from most conventional superconductors containing transition metals. 
The discovery of the superconductivity of magnesium diboride (MgB2) has caused a sensation in the field of condensed matter physics, as it has set a new record for the transition temperature of intermetallic superconducting materials, reaching up to 39K. Unlike alloy based low-temperature superconducting materials, it can operate in the working temperature range of refrigerators (20-30K), thereby reducing the expensive cost of liquid helium cooling in this temperature range. Although oxide high-temperature superconductors have the advantage of high superconducting transition temperature, their small coherence length leads to low condensation energy and magnetic flux pinning energy; Layered structure leads to anisotropy; The characteristics of ceramics make materials prone to brittle cracking and the raw material prices are relatively expensive, which greatly limits their application. Compared with ceramic high-temperature superconducting materials, MgB2 is easier to form, has weaker anisotropy, and has a longer coherence length, which makes MgB2 have good application prospects.   
The measured combustion calorific value and combustion efficiency of MgB2 are higher than those of amorphous boron In the temperature range of 298-1673 K, the thermal oxidation reaction of MgB2 under slow heating conditions consists of four stages, with the main oxidation heat release and weight gain occurring between 1200-1665 K The main oxidation heat release and weight gain of amorphous boron occur around 1919 K At 1665 K, the oxidation rate of MgB2 is as high as 94.3%, while the oxidation rate of amorphous boron is only 43.6% Compared with amorphous boron, MgB2 can be fully oxidized at lower temperatures and has better thermal oxidation characteristics than amorphous boron. 
The superconducting principle of MgB2 is similar to that of metals, which is formed by the quantized vibration of sound to connect electricity into pairs and form superconductivity through the material in the form of sound waves. Therefore, it belongs to the BCS theory category. The BCS theory was developed by Bardeen in 1957 The theory proposed by Kubo and Schreiffer to explain conventional superconductors The classical theory of electro acoustic coupling is based on the theory of electron phonon coupling The explanation of superconductivity based on action provides a good explanation for the superconductivity of metals and intermetallic compounds. Research has shown that (1) the superconducting source of MgB2, JB, has a high phonon spectrum and superconducting current density, and the grain boundary is relatively "transparent" to the superconducting current. That is, the superconducting current is not limited by the connectivity of the material boundary, making it particularly suitable for strong electric transport and the production of high-quality microwave devices. Secondly, due to the relatively cheap raw materials B. Mg used in the preparation of MgB2, the synthesis is also simple; while oxide high-temperature superconductors are composed of multiple elements. The raw materials are expensive and brittle, making it difficult to process into practical wires. In short, the weakness of MgB's low critical temperature may be compensated for by its advantages in preparation, processing, and price. Table 1 shows the basic performance indicators of MgB2. The current research status of the superconducting properties of 3MgB2. Currently, research in various countries mainly focuses on the influencing factors of the critical temperature of MgB2. So that it can be put into use as soon as possible. Scientists usually use two "doping" methods to change the critical temperature of MgB2: 1 The species is electron doped, synthesized MgB, -, X, (X=Be C. N.O, etc.), i.e. using Be C. Elements such as N.O partially replace the B element in MgB2, and so far no electron doping has been found to have the effect of increasing the critical temperature. Another type is vacancy doping. Synthesis of Mg M.B2(M= Al. Be . Ca, Cu, Ll. Na. Zn, etc.), i.e. using Al, Be Ca . Cu, Ll, Na, Zn and other elements partially replace Mg element. Doping or substitution can change the carrier concentration of the material, thereby altering Tc. Chinese scientists have discovered that MgB (i.e. Mgo, CuoxB2) doped with 20% copper element has superconductivity, with a superconducting transition starting temperature of 49K The zero resistance temperature is 45.6K Currently, MgoCuozB2 has the highest critical temperature among the new type of superconductors based on magnesium oxide. MgoCuozB2 is mainly a mixture of MgB2 and CuzMg, and its crystal structure is still hexagonal, but its c-axis and a-axis are slightly shorter than those of MgB2. The Organizational Structure and Synthesis Method of MgB2 
MgB2 is a simple binary compound belonging to the hexagonal crystal system, with an A1B2 type simple hexagonal structure and a P6/mmm space group. This structure contains a graphite like B layer, with a hexagonal tightly packed Mg atomic layer between two B atomic layers, where Mg atoms are located at the center of the hexagon formed by B atoms. The interplanar spacing of boron atoms in MgB2 crystals is significantly larger than the atomic spacing, resulting in a higher coefficient of thermal expansion on the C-axis compared to the A-axis. 
Principle and Basic Properties of MgB2 Superconductivity 
Compared with the critical temperature of existing complex oxide superconductors reaching up to 160K, the critical temperature of MgB is not considered high. Why can it cause such a big sensation and response? One reason is that it is similar to complex oxide high-temperature superconductors MgB: It is a simple binary compound It is a standard isotropic first class hyperconservative.