Development of Doped ${\rm MgB}_{2}$ Wires and Tapes for Practical Applications

A review of current developments in the study of chemical doping effect on the superconducting properties of MgB₂ wires and tapes is presented, based on the known literature data and our own results. The critical current density of MgB₂ can be improved through various kinds of dopants. Among these dopants, doping with carbon-containing materials seems to be the most effective way to improve the J_c performance. The doping effect of carbon in different forms and carbon-based compounds such as SiC, nano-C, metal carbides, as well as aromatic hydrocarbon and carbohydrate on the J_c-B characteristics of MgB₂ was discussed in detail. The C can be incorporated into the MgB₂ crystal lattice by replacing boron, and thus Bc₂ is significantly enhanced due to selective tuning of impurity scattering of the ?? and ?? bands in the two-band MgB₂. Besides the efforts of increasing Bc₂ by carbon doping, the fine grain size and nano-size inclusions caused by doping would create many flux pinning centers improving the J_c-B property of MgB₂. Based on these considerations, we suggested some principles for the selection of dopants.