Improved critical current densities in ex situ processed MgB₂ tapes fabricated with chemically treated powder

Fe-sheathed MgB₂ tapes were fabricated using powder chemically treated through an ex situ process employing a powder-in-tube (PIT) technique. The treatment of MgB₂ powder in a benzene solution of benzoic acid caused the pulverization and disappearance of large grains. Compared with the pristine powder without treatment, the tape made from this powder showed a fivefold increase in critical current density (J_c) in 10 T. This was due to the pulverization of grains by the chemical treatment and the removal of surface MgO layers from MgB₂ grains by dissolution in the acid solution. The removal of MgO layers was effective in promoting substitution of carbon from the solvent for boron.