Study On The Phase Purity And Microstructure Of MgB₂ Superconductor

The discovery of MgB₂ superconductor, a binary intermetallic, in 2001 in Japan produced a boom in applied superconductivity research, and has caused an extensive interest either in both applied research field and the field of basic research. MgB₂ is a typical type II superconductor, its high Tc, simple crystal structure, large coherence length, and high critical current density, transparency of grain boundaries promise that MgB₂ will be a good candidate material for both large scale applications and electronic devices.A foundation for application of superconductors is the preparation of wires with high purity. In this research, starting from the heat treatment parameters, the purity and microstructure of forming MgB₂ has been studied. With the help of modern analytical instruments, improved synthesis technology of the Mg-B, such as simplified PIT method using a stainless steel tube, has enhanced its mechanical performance by using network & tape structure (copper tape, copper mesh, SS mesh), then analyzed the effects of the purity and microstructure.The results show that: atomic ratio of Mg: B = 1:2, mixed powders fully, heated to 650°C for 2 hours directly, finally we can obtained pure MgB₂ powders. Using SS tube into PIT method, the process of swagger is omitted, but its density is still assured, and also received high purity MgB₂ wires. Network & tape material have been used in the experiments. And the XRD patterns of Cu tape and Cu networks all show that Cu atoms haven't substitute Mg site in MgB₂, but exist in the form of MgCu2 and Mg2Cu (partly) in the samples according to the comparison of peak shape and Mg-Cu phase diagram. On the one hand, its existence restrained connectivity of MgB₂ grains; on the other hand, it could be used as new flux pinning center to improve superconducting properties. When using SS mesh, MgB₂ formed in the mesh; as a new synthesis, it would improve the mechanical properties and can effectively reduce the weak links.Furthermore, protecting Mg oxidation and volatilization at elevated temperature and avoid MgB₂ decomposing at high temperature are the key factors of preparation of MgB₂. Therefore the process must be protected by flowing Ar gas. Improving the density of bulks is important. The reason is porosity reduces the transport Jc in MgB₂. And rolling in PIT method, secondary sintering can reach the target.