Effect of carbon-doping in bulk superconducting MgB2 samples

Bulk superconducting samples of MgB2 were prepared by solid state reaction of stoichiometric quantities of Mg turnings and B in a sealed Ta cylinder a t 890 degreesC for 2 h. The "as-synthesized" MgB2 samples had a T-c of 39 K , as defined as the onset of diamagnetism. The crystal symmetry was found t o be hexagonal with lattice parameters, a = 3.0856 Angstrom, and c = 3.5199 Angstrom, similar to the literature values. To study the effect of carbon- doping in MgB2 various C-containing samples of I varying from 0 to 1.00 in MgB2-xCx were prepared. Magnetic characterizations indicate that the T, ons et is same for pure and C-doped samples for x = 0.05 and 0.10. However, the shielding signal decreased monotonically with C content, apparently due to the presence of carbon on the grain boundaries that isolates grains and pr events flow of supercurrents on the perimeter. Published by Elsevier Scienc e B.V.