Effect of carbon black doping on the microstructure and critical properties of MgB2 superconductor

Abstract

We selected amorphous, nano-size carbon black (10-30 nm) as a dopant for MgB2 superconductor to improve critical current density (J(c)) at high magnetic field. We fabricated the MgB2-xCx (x = 0, 0.01, 0.05, and 0.1) bulk superconductors using an in situ technique and evaluated the effects of doping on phase formation, microstructure, and critical properties. As the nominal C content increased from x = 0 to 0.1, the a-axis lattice parameter decreased, while the c-axis lattice parameter remained relatively unchanged. The T-c decreased from 37.2 to 35.1 K with increasing C content from 0 to 0.1. The decrease in T-c decreased with increasing C content. On the other hand, the J(c) value of the doped samples decreased more slowly with increasing magnetic field and had higher value at a high magnetic field than that of the undoped samples. This suggests the carbon black to be an effective dopant for improving the J(c) of MgB2 at high magnetic field. (C) 2008 Elsevier B.V. All rights reserved.