We present details of synthesis optimization and physical properties of nearly single phase carbon doped MgB2 with a nominal stoichiometry of Mg(B{0.8}C{0.2})2 synthesized from magnesium and boron carbide (B4C) as starting materials. The superconducting transition temperature is ~ 22 K (~ 17 K lower than in pure MgB2). The temperature dependence of the upper critical field is steeper than in pure MgB2 with Hc2(10K) ~ 9 T. Temperature dependent specific heat data taken in different applied magnetic fields suggest that the two-gap nature of superconductivity is still preserved for carbon doped MgB2 even with such a heavily suppressed transition temperature. In addition, the anisotropy ratio of the upper critical field for T/Tc ~ 2/3 is gamma ~ 2. This value is distinct from 1 (isotropic) and also distinct from 6 (the value found for pure MgB2).
Cite
@article{arxiv.cond-mat/0210530,
title = {Carbon doping of superconducting magnesium diboride},
author = {R. A. Ribeiro and S. L. Bud'ko and C. Petrovic and P. C. Canfield},
journal= {arXiv preprint arXiv:cond-mat/0210530},
year = {2009}
}