High critical current density of MgB2 bulks sintered in flowing welding grade Ar atmosphere
The effect of processing atmosphere on the microstructure and superconducting properties of MgB2 was studied for bulk samples made using the in situ reaction technique under argon gas with three different levels of purity: ultra-high, high, and welding grade. The critical temperature, Tc, decreased by 0.5 K, while the full width at half maximum (FWHM) of the MgB2 peaks, and the resistivity showed an increase in the sample processed in welding Ar. The critical current density, Jc, and the upper critical field, Hc2, for the welding Ar sample were improved in comparison with the samples treated in ultra-high and high purity argon. Optimal Jc in MgB2 can be achieved by using readily available and economical welding grade Ar as the protective atmosphere instead of using ultra-high or high purity Ar.