  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 Jc 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 Jc-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 two 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 centres improving the Jc-B
property of MgB2. Based on these considerations, we suggested some principles
for the selection of dopants.
