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

Abstract We report the fabrication of high-performance MgB 2 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 MgB 2 . 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 MgB 2 , significantly high current-carrying capability ( J c (5 K, 8 T) ∼3.1 × 10 4 A/cm 2 and J c (20 K, 6 T) > 10 3 A/cm 2 ) was obtained for aC-doped MgB 2 , which is comparable to the record high in-field J c reported for SiC-doped MgB 2 and much better than those reported in literature with other C sources. Furthermore, significant improvement in H irr and H c2 were also observed for aC-doped MgB 2 . The improved high-field properties in PMMA-derived aC-doped MgB 2 bulk suggest that the solution process could be a powerful technique to obtain uniform mixture of C-coated B to develop high-performance Mg(B 1− x C x ) 2 wires for practical applications.