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

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 Tc decreased from 37.2 to 35.1 K with increasing C content from 0 to 0.1. The decrease in Tc decreased with increasing C content. On the other hand, the Jc 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 Jc of MgB2 at high magnetic field.