The isotope effect of boron on the carbon doping and critical current density of Mg11B2 superconductors
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 (Jc) performance of MgB2, which is of great importance in terms of electromagnetic applications. In the present work, the isotope effect of 11B on carbon doping and Jc of MgB2 superconductors was for the first time studied systemically. It is found that as the chemical activity of 10B is higher than 11B, the substitution of B by C can more easily occur on 10B than on the 11B site of the MgB2 lattice. This is why carbon doping fails to increase the Jc value of isotope Mg11B2 superconductors. Our result is quite different from the case in carbon doped normal MgB2 superconductors with a natural boron source (composed of 10B-18.98% and 11B-81.02%) reported in most previous studies, where C can substitute a part of 10B 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.