Preparation and Flux Pinning Mechanism of C₆H₆-doped MgB₂ Superconductor Bulk

C₆H₆-doped MgB₂ superconductor bulks were synthesized by ball milling subsequently solid state sintering using magnesium powder (Mg), boron powder (B) and benzene (C₆H₆) as raw materials. The effects of C₆H₆ doping on phase evolution, microstructure and the critical current density J_c of MgB₂ were investigated. The results show that C₆H₆ doping has little effect on the formation temperature of MgB₂. C enters the lattice of MgB₂ by substitution for B, which makes the decreasing of lattice constant a and the grain size refines gradually. C₆H₆-doped MgB₂ sample with molar fraction of 0.04 has relatively low superconducting transition critical temperature T_c of 31 K, but exhibits the excellent J_c. At high temperature 20 K and high magnetic density 2 T, J_c remains at 3.6×10⁴ A/cm², which is mainly due to hybrid flux pinning mechanism of grain boundary pinning and point pinning.