TY - JOUR
T1 - Microstructural connectivity in sintered ex-situ MgB2 bulk superconductors
AU - Shimada, Yusuke
AU - Hata, Satoshi
AU - Ikeda, Ken Ichi
AU - Nakashima, Hideharu
AU - Matsumura, Syo
AU - Tanaka, Hiroya
AU - Yamamoto, Akiyasu
AU - Shimoyama, Jun Ichi
AU - Kishio, Kohji
N1 - Funding Information:
This work at the Kyushu University was partly supported by the Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS) (Grant Nos. 22102002 and 25286027 ) and by Nanotechnology Support Project of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. The work at the University of Tokyo was supported by the Japan Science and Technology Agency , PRESTO , and by the JSPS (Grant No. 24656368 ).
Publisher Copyright:
© 2015 Elsevier B.V. All rights reserved.
PY - 2016/1/25
Y1 - 2016/1/25
N2 - 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.
AB - 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.
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U2 - 10.1016/j.jallcom.2015.09.253
DO - 10.1016/j.jallcom.2015.09.253
M3 - Article
AN - SCOPUS:84943603511
SN - 0925-8388
VL - 656
SP - 172
EP - 180
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
ER -