Effect of sintering time on superconductivity in MgB2

We studied the effect of sintering time on microstrain, critical current density (Jc), and resistivity (ρ) in MgB2 bulks. All samples were fabricated by solid state reaction and sintered within a time range of 30 minutes – 60 hours. It has been found that microstrain increases as the sintering time increases, while the connectivity decreases with sintering time from 30 minutes to 20 hours, and then increases to 60 hours. Both the irreversibility field, Hirr, and the upper critical field, Hc2, were increased with microstrain. This indicates that the disorder significantly affects Hirr and Hc2. The sample with the sintering time of 30 minutes exhibited the highest Jc at all fields, due to its having the highest connectivity. When the sample is sintered for a very long time (60 hours), Jc at high fields can be improved. This is mainly attributed to increased Hc2.