Towards the Realization of Higher Connectivity in MgB2Conductors: In-situ or Sintered Ex-situ?

The two most common types of MgB2conductor fabrication technique –in-situandex-situ– show increasing conflicts concerning the connectivity, an effective current-carrying cross-sectional area. Anin-situreaction yields a strong intergrain coupling with a low packing factor, while anex-situprocess using pre-reacted MgB2yields tightly packed grains, however, their coupling is much weaker. We studied the normal-state resistivity and microstructure ofex-situMgB2bulks synthesized with varied heating conditions under ambient pressure. The samples heated at moderately high temperatures of ∼900 °C for a long period showed an increased packing factor, a larger intergrain contact area and a significantly decreased resistivity, all of which indicate the solid-state self-sintering of MgB2. Consequently the connectivity of the sinteredex-situsamples exceeded the typical connectivity range 5–15% of thein-situsamples. Our results show self-sintering develops the superior connectivity potential ofex-situMgB2, though its intergrain coupling is not yet fulfilled, to provide a strong possibility of twice or even much higher connectivity in optimally sinteredex-situMgB2than inin-situMgB2.