Magnesium diboride is an inorganic compound with the formula MgB₂. Amorphous magnesium diboride is a dark gray, water-insoluble, granular solid. In 2001, researchers discovered that magnesium diboride transforms into a superconductor at 39 Kelvin, making it a regular superconductor. MgB₂ differs significantly from most conventional superconductors that contain transition metals.

The discovery of the superconductivity of magnesium diboride (MgB2) caused a stir in the condensed matter physics community, because it set a new record for the transition temperature of superconducting materials in intermetallic compounds, with the superconducting transition temperature as high as 39K. Unlike alloy-type low-temperature superconducting materials, it can work in the operating temperature zone of the refrigerator (20-30K), thereby reducing the cost of expensive liquid helium temperature zone refrigeration. Although oxide high temperature superconductors have the advantage of high superconducting transition temperature, the condensation energy and magnetic flux pinning energy are low due to small coherence length. Layered structure leads to anisotropy. The characteristics of ceramics make the material easy to crack and the raw material price is relatively expensive, etc., which is greatly limited in application. MgB2 is easy to form, weak anisotropy and large coherence length compared with ceramic high temperature superconducting materials, which makes MgB2 have a good application prospect.

The measured 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 the condition of slow warming consists of four stages, and the main oxidation heat release and weight gain occur between 1200 ~ 1665 K. The main oxidative heat release and weight gain of amorphous boron occurred around 1919 K. At 1665 K, the oxidation rate of MgB2 reached 94.3%, while that of amorphous boron was only 43.6%. Compared with amorphous boron,MgB2 can be fully oxidized at a lower temperature, and the thermal oxidation characteristics are better than amorphous boron.

The superconductivity principle of MgB2 is similar to that of metal, which is connected by the quantized vibration of sound into pairs, and forms superconductivity through the material in the form of sound waves, so it belongs to the category of BCS theory. BCS theory was developed by Bardeen in 1957. Cooper and Sherif's theory to explain conventional superconductors. Both classical electroacoustic coupling theory, to the electron phonon phase. It explains the superconductivity of metals and intermetallic compounds well. The results show that (1) the superconductivity source of MgB2 is original phonon spectrum, and the superconducting current density is high, and the grain boundary is "transparent" relative to the superconducting current. That is, the superconducting current is not limited by the connectivity of the product, which is especially suitable for the transmission of strong electricity and the manufacture of high-quality microwave devices. The second reason is that the preparation material B.MGB2 is relatively cheap and the synthesis is simple; Oxide high temperature superconductors are composed of a variety of elements. The raw material is expensive, and the material is brittle: large, difficult to process into practical wire. In short, the weakness of MgB's low critical temperature may be compensated for by its advantages in preparation, processing, price, etc. Table 1 shows the basic performance indicators of MgB2. Research status of 3MgB2 superconductivity. At present, the research content of various countries mainly focuses on the influencing factors of MgB2 critical temperature. So that we can make it practical as soon as possible. Scientists usually use two "doping" methods to change the critical temperature of MgB2: one is electron doping, synthesizing MgB,-,X,(X= Be.C.N.O, etc.), that is, to partially replace the B element in MgB2 with elements such as Be.C.N.O. So far, no electron doping has been found to increase the critical temperature: the other It's empty six doping. Synthetic Mg... M.B 2 (M = Al. Be. Ca, Cu, Ll. Na, zinc, etc.), which is Al, Be, Ca, Cu, Ll. Na. Partly replace Mg element zinc and other elements. The carrier concentration of the material can be changed by doping or substitution, thereby changing the Tc. Chinese scientists found that MgB doped with 20% copper (Mgo,Cuo xB2) has superconductivity, and its superconducting transition starting temperature is 49K. The zero resistance temperature is 45.6K, which is the highest critical temperature among the new magnesium superconductors at present." MgoCuozB2 is mainly a mixture of MgB2 and CuzMg, and its bulk structure is still hexagonal, but its C-axis and A-axis are slightly shorter than MgB2. Structure and synthesis of MgB2
MgB2 is a simple binary compound, belonging to the hexagonal crystal system,A1B2 simple hexagonal structure, with P6/mmm void group. This structure contains a graphite-like B layer, and in between the two B layers there is a hexagonal tightly packed Mg atom layer,Mg atom at the center of the hexagonal shape formed by B and f. The surface spacing of boron atoms in MgB2 crystal is obviously larger than the atomic spacing, so that the thermal expansion coefficient of C-axis is larger than that of A-axis.

Principle and basic properties of MgB2 superconductivity
Compared with the critical temperature of the existing complex oxide superconductors up to 160K, the critical temperature of MgB is not high, why can it cause such a stir and response? One is because it is similar to complex oxide high-temperature superconductors. MgB: is a simple binary compound. It is a standard isotropic superheron of the first kind.