Stoichiometry dependence of the critical current density in pure and nano-SiC doped MgB2/Fe tapes

The stoichiometry dependence of the microstructure and superconducting properties of pure and nano-SiC doped MgB₂/Fe tapes was systematically investigated. The tapes prepared with the composition of a slight deficiency of Mg (Mg_0.9B₂ and Mg_xB₂(SiC)_0.1 (x = 0.9 and 1.0)) showed the best transport J_c. Adding a slight excess of Mg like 5%, as being done by many researchers, was not beneficial for the J_c improvement as expected. The onset T_c was not significantly changed in both doped and undoped tapes by adding excess of boron or magnesium, but the transition widths were broadened due to the induced impurities. The slightly-Mg-deficient pure samples show smaller grain sizes, which corresponds to a better J_c–B performance at high magnetic field due to the enhanced grain boundary pinning. The field dependence of J_c in nano-SiC doped tapes was almost not influenced by varying the starting Mg content although microstructural difference can still be seen, suggesting that the flux pinning ability was mainly controlled by the carbon substitution effect for boron.