Solution-processed nanometers thick amorphous carbon-coated boron as an efficient precursor for high-field performance of MgB2

We report the fabrication of high-performance MgB2 bulk superconductors doped with amorphous carbon (aC), derived from PMMA polymer, a safe and cost effective carbon source as compared to explosive gaseous and expensive C-containing nanoadditives. The commonly used C-containing nanoadditives and boron (B) precursor nanopowders are usually prone to agglomeration in solid state mixing which causes poor reactivity and non-uniform distribution that leads to deterioration of critical current properties of MgB2. We have overcome this problem by achieving uniform 3-4 nm thin coating of aC on B nanopowders by pyrolysis of PMMA through solution process. Compared to undoped MgB2, significantly high current-carrying capability (Jc (5 K, 8 T) ∼3.1 × 104 A/cm2 and Jc (20 K, 6 T) > 103 A/cm2) was obtained for aC-doped MgB2, which is comparable to the record high in-field Jc reported for SiC-doped MgB2 and much better than those reported in literature with other C sources. Furthermore, significant improvement in Hirr and Hc2 were also observed for aC-doped MgB2. The improved high-field properties in PMMA-derived aC-doped MgB2 bulk suggest that the solution process could be a powerful technique to obtain uniform mixture of C-coated B to develop high-performance Mg(B1−xCx)2 wires for practical applications.