Abstract
The relationship between the reactivity, doping effects of metal carbide and superconducting properties of MgB2 were studied to investigate the intrinsic carbon substitution effects on the critical current properties of MgB2. Decreases in Tc and a-axis length of MgB2 due to the carbon substitution were observed. We found that only a part of the carbon in nominal composition was actually substituted into the MgB2 lattice and that not nominal but actual carbon content in MgB2 lattice played an essential role for determining the lattice properties and superconductivity of MgB2. Improved field dependence of Jc was observed in carbide doped MgB2 bulk samples especially at low-temperatures under high magnetic fields. On the other hand, surplus doping of carbide was found to decrease Jc due to serious suppression of Tc and a reduction in the effective current path. These findings suggested that optimizing the actual carbon content by selecting suitable carbon source dopants and heating conditions is important for improving the critical current properties of superconducting MgB2 materials.
