The isotope effect of boron on the carbon doping and critical current density of Mg11B2 superconductors

Abstract

Previous works mainly focused on the isotope effect of boron on the T_c 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 ¹¹B on carbon doping and J_c 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 J_c 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 J_c performance at high fields. Our results provide a deeper understanding on the boron isotope effect and chemical doping mechanism in MgB₂ superconductors.