Effect of Sintering Time on the Optimal Synthesis Condition in MgB ₂

The present investigation has focused on methods to improve the critical current density (J _c ) of the disk-shape bulk MgB ₂ superconductor by optimizing sintering conditions. The samples have been synthesized using a two-step process. The samples are sintered at 775 ^o C for 3 h in pure argon atmosphere, followed by re-sintering at 660 ^o C for 24 to 100 hours. X-ray diffraction showed that all the samples re-sintered are single phase and homogenous. The magnetization measurements confirm a sharp superconducting transition with T _c (onset) at around 37 K. The critical current density (J _c ) for MgB ₂ samples increases with increasing the re-sintering time at 660 ^o C, in that the highest J _c value of 170 kA/cm ² at 20 K was obtained in the sample re-sintered at 660 ^o C for 100 h.