Effects of Si and C Doping on the Superconducting Properties of MgB2.

C and Si powders of different sizes were doped into MgB2 separately or together. Samples were made by a solid-state reaction method. It was found that the C doping had a strong negative effect on critical temperature (Tc) while the Si doping did not significantly depress Tc. All of these doping materials increased Jc at higher fields when the doping particles were of nanometer sizes. At 20 K and 4 T, Jc of the sample doped with nano-Si achieved 104A/cm2, which is 2 orders of magnitude higher than that of coarse Si doped MgB2. Jc of the sample doped with nano-carbon is one order of magnitude higher than for the sample doped with coarse carbon particles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]