부산대학교 도서관

The effects of the heat treatment temperature (600℃-1050℃) on the formation of MgB2 and the superconducting properties have been examined. The self-synthesized MgB4 and commercial Mg powders were used as raw materials for the formation of MgB2. The superconducting critical temperatures (Tcs) of MgB2 bulk superconductors prepared at 600℃-850℃ were as high as 37-38 K regardless of the heat treatment temperature. However, because MgB4 is more stable than MgB2 at above 850℃, no superconducting signals were detected in the susceptibility-temperature curves of the samples prepared above 850℃. As for the critical current density (Jc), the sample heat-treated at a low temperature (600℃) for a prolonged period (40 h) showed a Jc higher than those prepared at 650℃-850℃ for a short period (1 h). The FWHM (full width at half maximum) result showed that the grain size of MgB2 of the 600℃ sample was smaller than that of the other samples. The high Jc of the 600℃sample is attributed to the presence of large numbers of grain boundaries, which can act as flux pinning centers of MgB2.