Carbon was substituted into the MgB2 lattice, to form Mg(B1-xCx)2, by heat treatment in sealed Ta tubes; starting with the elemental constituents. The superconducting transition temperature, TC, was measured via diamagnetic susceptibility. The superconducting transitions were sharp and X-ray diffraction from the samples exhibited only trace amounts of impurity phases. The C fraction substituted for B atoms in the MgB2 lattice, as deduced from a well-established correlation between the a lattice parameter and x in Mg(B1-xCx)2, was found to be very close to the target values. The temperature dependence of the normalized resistance was similar to that seen in C-doped MgB2 single crystals along the ab plane. Rn/R(300K), where Rn was the resistance just above TC, increased with x.

Stoichiometric Carbon Substitution in MgB2. S.J.Balaselvi, N.Gayathri, A.Bharathi, V.S.Sastry, Y.Hariharan: Superconductor Science and Technology, 2004, 17, 1401-5