Microstructural connectivity in sintered ex-situ MgB2 bulk superconductors

Yusuke Shimada, Satoshi Hata, Ken Ichi Ikeda, Hideharu Nakashima, Syo Matsumura, Hiroya Tanaka, Akiyasu Yamamoto, Jun Ichi Shimoyama, Kohji Kishio

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17 Citations (Scopus)


We have performed combined high-resolution microstructural and grain orientation analyses to understand the key microstructural factors associated with high intergranular transport current in polycrystalline bulk forms of MgB2. The ex-situ method can produce MgB2 with relatively high packing factors; nevertheless, the connectivity of MgB2 fabricated by the ex-situ method (ex-situ MgB2) was less than that of in-situ MgB2. The poor connections between MgB2 grain aggregates cause the low connectivity of ex-situ MgB2. Plate-like pores are present between the aggregates of MgB2 grains in ex-situ MgB2; these pores remain even after prolonged self-sintering at high temperatures. In addition, MgB2 crystals decompose to MgB4 in sintering for a long period. Moreover, MgO particles are formed between MgB2 grain aggregates and inhibit interaggregate connections. In contrast, in-situ MgB2 fabricated at the same sintering conditions exhibits spherical pores between MgB2 grains, resulting in a uniform pore distribution and intergranular connection. These problems must be addressed to further enhance the connectivity in ex-situ MgB2.

Original languageEnglish
Pages (from-to)172-180
Number of pages9
JournalJournal of Alloys and Compounds
Publication statusPublished - 2016 Jan 25


  • Electron microscopy
  • MgB superconductor
  • Microstructural connectivities
  • Polycrystalline bulk
  • Self-sintering


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