Sugar as an optimal carbon source for the enhanced performance ofMgB2 superconductors at high magnetic fields

Abstract

In this paper we report the results of an extended study of the effectof sugar doping on the structural and electromagnetic properties ofMgB2 superconductors. High values of the upper critical field(Bc2) of 36 T and theirreversibility field (Birr) of 27 T have been estimated at the temperature of 5 K in a bulkMgB2 sample with the addition of 10 wt% of sugar. The critical current density(Jc(Ba)) ofsugar-doped samples has been significantly improved in the high field region. The value of transportJc has reachedas high as 108 A m−2 at 10 T and 5 K for Fe-sheathed sugar-dopedMgB2 wire. The analysis of the pinning mechanism in the samples investigated indicatedthat dominant vortex pinning occurs on the surface type of pinning defects, suchas grain boundaries, dislocations, stacking faults etc, for both pure and dopedMgB2.In sugar-doped samples, pinning is governed by numerous crystal lattice defects, which appear inMgB2 grains as a result of crystal lattice distortion caused by carbon substitution forboron and nano-inclusions. The drastically improved superconducting properties ofsugar-doped samples are also attributed to the highly homogeneous distribution andenhanced reactivity of this dopant with host Mg and B powders. The resultsof this work suggest that sugar is the optimal source of carbon for dopingMgB2 superconductor, especially for application at high magnetic fields.