The upper critical field of polycrystalline wire segments was increased to nearly 36T by the substitution of 5.2%C for B. Fabrication details and physical properties of Mg(B1−xCx)2 were presented for x-values of up to 0.052. The C doping was achieved using a 2-step reaction technique which involved an initial C doping of B wire segments using chemical vapor deposition followed by exposure of the C-doped B segments to Mg vapor. The C content was determined by the relative contraction of the a-lattice parameter. The superconducting transition temperature was suppressed by approximately 1K/%C while HC2c (T = 0) rose at a rate of nearly 4T/%C.

Synthesis and Optimization of Mg(B1−xCx)2 Wire Segments. R.H.T.Wilke, S.L.Budko, P.C.Canfield, D.K.Finnemore, R.J.Suplinskas, S.T.Hannahs: Physica C, 2005, 424[1-2], 1-16