Benzoic Acid Doping to Enhance Electromagnetic Properties of MgB2 Superconductors

The effect of benzoic acid doping on lattice parameters, microstructure, critical temperature (T_c), critical current density (J_c) and flux pinning force of MgB₂ has been studied. In this work we used benzoic acid as an example of aromatic acids as an additive to MgB₂. For different sintering process, actual carbon (C) substitution for boron (B) was estimated to be from 3.5 at% to 5.0 at% of B while T_c dropped about 2-4 K. The advantages of aromatic acid doping include homogeneous mixing of precursor powders, avoidance of expansive nano-additives, production of highly reactive C and significant enhancement in J_c of MgB₂, compared to undoped samples. High level C substitution of B can induce the MgB₂ crystals grow into bar shape microstructure. The J_c value of 1.5 times 10⁴ Acm^-2 at 5 K and 8 T for preheated 10 wt% C₇H₆O₂ doped MgB₂ sample is higher than that of the undoped MgB₂ by a factor of 13. As there are numerous aromatic acids readily available this finding has significant ramifications not only for the fabrication of MgB₂ but also for many C based compounds and composites.