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Maeda, Minoru,Choi, Seyong Elsevier 2019 Journal of alloys and compounds Vol.787 No.-
<P><B>Abstract</B></P> <P>Carbon-based organic molecular gas is a well-known chemical agent for controlling inorganic structures of MgB<SUB>2</SUB> single-crystal material. The utilization of such a gas can also be applied to polycrystalline materials. So far, however, few studies have dealt with the methodology and the effects, especially the structural mechanism. Herein, we have focused on hydrocarbon gas as an active carbon source for bulk and wire materials consisting of MgB<SUB>2</SUB> polycrystals. A starting material, amorphous or crystalline boron powder, was heated and exposed to the molecular gas in argon atmosphere. While the treated powder showed no major change in its structure, as characterized by X-ray diffraction profiles, its usage as a precursor powder for MgB<SUB>2</SUB> bulks resulted in a marked increase in the in-field critical current density. In order to examine and help identify the underlying causes, we have carried out further structural analysis with the Halder Wagner method, considering the integral breadths of peaks in the X-ray diffraction profiles. Finally, the gas treatment was found to improve the in-field transport properties, even for MgB<SUB>2</SUB> wires and densified conductors, which are made from crystalline boron powder.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Carbon-based organic molecular gas can be utilized for MgB<SUB>2</SUB> bulk and wire materials. </LI> <LI> The precursor powder doesn't show major structural change after the gas treatment. </LI> <LI> In contrast, the structural order in MgB<SUB>2</SUB> lattice is lowered by the gas treatment. </LI> <LI> The modified structure leads to enhancement in the in-field transport property. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Preferential growth of boron layer in magnesium diboride (MgB<sub>2</sub>) by Mg diffusion method
Heo, Yoon-Uk,Yoon, Sangmoon,Kim, Jung Ho,Kim, Young-Ki,Kim, Miyoung,Song, Tae-Jin,Maeda, Minoru,Dou, Shi Xue Elsevier 2017 Journal of alloys and compounds Vol.725 No.-
<P><B>Abstract</B></P> <P>Growth mechanism and grain boundary (GB) contact of polycrystalline MgB<SUB>2</SUB> fabricated by Mg diffusion method are studied by STEM and EELS analyses. In contrast to the previous reports based on the computational calculation, preferential growth of (001) boron (B) layer and the B-B contact at MgB<SUB>2</SUB> GBs are confirmed by annular dark field (ADF) –STEM image and the combined EELS analyses. The effect of B-B contact at the GB on the superconductivity is further evaluated using First principles calculation. Superior GB linkage of the supercurrent flow via GB B-B contact is expected from the calculated density of states at Fermi level. B-terminated growth mechanism in Mg diffusion method and the effect of GB connectivity via B-B and Mg-Mg contacts are discussed. Finally, we suggest a model of GB linkage of supercurrent flow via B-B contact in polycrystalline MgB<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Preferential growth of boron in polycrystalline MgB<SUB>2</SUB> has been firstly confirmed. </LI> <LI> The B-terminated growth mechanism of an MgB<SUB>2</SUB> has been suggested. </LI> <LI> The GB linkage via B-B contact in polycrystalline MgB<SUB>2</SUB> has been elucidated. </LI> </UL> </P>
Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi
Kim, Jung Ho,Oh, Sangjun,Heo, Yoon-Uk,Hata, Satoshi,Kumakura, Hiroaki,Matsumoto, Akiyoshi,Mitsuhara, Masatoshi,Choi, Seyong,Shimada, Yusuke,Maeda, Minoru,MacManus-Driscoll, Judith L,Dou, Shi Xue Nature Publishing Group 2012 NPG Asia Materials Vol.4 No.-
Tailored Materials for High‐Performance MgB<sub>2</sub> Wire
Kim, Jung Ho,Oh, Sangjun,Kumakura, Hiroaki,Matsumoto, Akiyoshi,Heo, Yoon‐,Uk,Song, Kyeong‐,Se,Kang, Yong‐,Mook,Maeda, Minoru,Rindfleisch, Matt,Tomsic, Mike,Choi, Seyong,Dou, Shi Xue WILEY‐VCH Verlag 2011 Advanced Materials Vol.23 No.42
<P><B>Carbon‐encapsulated crystalline boron nanopowder</B> and coarse magnesium powder are used as inexpensive tailored starting materials for the fabrication of high‐performance MgB<SUB>2</SUB> superconducting wire. A low sintering temperature leads to a high critical current density, as a result of nanometer‐sized boron powder, surface oxidation preclusion by carbon encapsulation, and grain alignment by elongated magnesium coarse powder.</P>