The discovery of superconductivity in MgB2 with an unusually high TC of 39 K interested material scientists all over the world. Many of its superconducting properties, including an experimentally observed double energy gap, differ significantly with those of conventional LTS and HTS. Many scientists proposed exotic and unconventional mechanisms to explain the superconductivity in MgB2, but after more than 5 years it is now accepted that MgB2 is a BCS type superconductor with exceptionally high TC. In this review we discuss qualitatively the origin of superconductivity in MgB2 based on both experimental and theoretical results. The variation of TC of MgB2 with various processes, such as irradiation of high energy ions, doping and external pressure, etc., is discussed and reviewed. TC of MgB2 decreases upon irradiation, by applying external pressure and by most of the doping. The reduction of density of states at the Fermi level, increased band scattering and changes in the phonon frequencies are the main factors which reduce the TC under these conditions.

A systematic study on the reactivity of commonly used sheath materials (Ag, Cu, Fe, SS, Ta and Ni) with Mg/B during in situ powder-in-sealed-tube processing of MgB2 superconductor was carried out at different temperatures. Characterization of the samples using XRD, SEM and EDS showed that the heat treatment temperature and type of metal sheath have profound influences on the reactivity. The quantitative data reported here are highly useful for choosing the right sheath material and processing temperature for the fabrication of high quality MgB2 based conductors.

We investigated the effect of doping of burned rice husk which contains ultrafine SiO2 and highly reactive carbon, on the crystal lattice and superconducting properties of MgB2 superconductor prepared by an in situ powder in sealed tube method. XRD, TEM, and magnetic measurements confirm the substitution of carbon atoms at boron sites in the MgB2 lattice and the formation of intragrain nanoinclusions in MgB2. From JC (H) characteristics, doped samples show a drastic enhancement of JC compared with pure MgB2. The enhancement of in‐field JC values is due to the flux pinning on lattice defects produced by C substitution and nanoscale inclusions of impurity phases.

We investigated the influence of reactivity of commonly used sheath materials (Fe, SS, Cu, and Ni) with Mg/B, processed by in situ powder in sealed tube method on superconducting properties of MgB2. X-ray diffraction characterization of samples yields quantitative data of the volume fraction of MgB2 core, whereas magnetic measurements show the influence of added sheath materials on TC , JC(H), Hirr, and flux pinning behavior of MgB2. Our comparative study gives better phase purity, JC(H) characteristics, and flux pinning behavior for Fe and SS added samples, which shows the suitability of Fe and SS as sheath materials in MgB2 wire/tape fabrication.