Effect of sintering temperature under high pressure on the superconductivity of MgB2

We report on the effect of sintering temperature on the superconductivity of ${\mathrm{MgB}}_{\mathrm{2}}$ pellets prepared under a high pressure of 3 GPa. The superconducting properties of the nonheated ${\mathrm{MgB}}_{\mathrm{2}}$ were poor. However, as the sintering temperature increased, the superconducting properties were vastly enhanced, which was demonstrated by the narrow transition width for the resistivity and the low-field magnetization. The observed surface morphology using scanning electron microscopy showed that these changes were closely related to changes in the microscopic level such as the connectivity of the grains.