Effect of citric acid doping on flux pinning in bulk MgB2 prepared by chemical solution route

In this paper, we study the doping effect of citric acid (C₆H₈O₇), from 0 to 30 wt% of the total MgB₂, on the properties, such as critical temperature (T_c), critical current density (J_c), irreversibility field (H_irr) and crystalline structure of MgB₂ superconductors. The XRD patterns of samples show a slightly decrease in the a-axis lattice parameter for doped MgB₂, due to the partial substitution of carbon at boron site. At 10 K the citric acid doped sample exhibits the J_c values greater than 3.4times10⁵ A/cm² in self-field, which is similar to the pure one while in high field region the J_c was increased by an order of magnitude in comparison to undoped one. For MgB₂ doped with 15 wt% citric acid, J_c still remains about 10³ A/cm² in 7 T at 10 K. In addition, the self-field J_c of citric acid doped sample is slightly reduced at additive level higher than 10%. The improved flux pinning behavior could easily be seen from reduced flux pinning force curves.