Effects of boron powder by hydrocarbon gas treatment on the structural and superconducting properties of in situ-processed MgB2 polycrystalline materials

Carbon-based organic molecular gas is a well-known chemical agent for controlling inorganic structures of MgB2 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 MgB2 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 MgB2 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 MgB2 wires and densified conductors, which are made from crystalline boron powder. (C) 2019 Elsevier B.V. All rights reserved.