The isotope effect of boron on the carbon doping and critical current density of (MgB2)-B-11 superconductors

Abstract

Previous works mainly focused on the isotope effect of boron on the Tc performance and superconducting mechanism of MgB2 superconductors but were never concerned with its effect on the chemical doping and critical current density (J(c)) performance of MgB2, which is of great importance in terms of electromagnetic applications. In the present work, the isotope effect of B-11 on carbon doping and Jc of MgB2 superconductors was for the first time studied systemically. It is found that as the chemical activity of B-10 is higher than B-11, the substitution of B by C can more easily occur on B-10 than on the B-11 site of the MgB2 lattice. This is why carbon doping fails to increase the Jc value of isotope (MgB2)-B-11 superconductors. Our result is quite different from the case in carbon doped normal MgB2 superconductors with a natural boron source (composed of B-10 -18.98% and B-11 -81.02%) reported in most previous studies, where C can substitute a part of B-10 and thus significantly improve Jc performance at high fields. Our results provide a deeper understanding on the boron isotope effect and chemical doping mechanism in MgB2 superconductors.