High critical current densities in bulk MgB₂ fabricated using amorphous boron

We prepared bulk MgB₂ from high-purity commercial powders of Mg metal (99.9% purity) and amorphous B (99% purity) powders using a single-step solid state reaction at 775°C for varying sintering duration from 1 to 10h in pure argon atmosphere. X-ray diffraction analysis showed that all the samples were single phase MgB₂. The magnetization measurements confirmed a sharp superconducting transition with T_c,onset at around 38.2-38.8K. The critical current density (J_c) values for the MgB₂ samples produced at 1h sintering time is the highest one in all processed materials here. Scanning electron microscopy analyses indicated that the sintering time has a crucial influence on the grain size. As a result, the highest J_c value of 270kAcm^-2 at 20K and self-field was achieved in the sample produced at 775°C for 1h. Our results clearly demonstrate that the optimization of the sintering conditions is essential to improve the bulk MgB₂ performance.