Mgb2 single crystal and its production method, and superconductive material containing mgb2 single crystal

Abstract

The invention is intended to establish means for manufacturing MB single crystals and to provide a useful superconductive material (wire rod and so forth) taking advantage of anisotropic superconductive properties thereof. A mixed raw material of Mg and B or a precursor containing MgB crystallites, obtained by causing reaction of the mixed raw material of Mg and B, kept in contact with hexagonal boron nitride (hBN), is held at a high temperature in the range of 1300 to 1700° C. and under a high pressure in the range of 3 to 6 GPa to cause reaction for forming an intermediate product, thereby growing the MB single crystals having anisotropic superconductive properties via the intermediate product. The single crystals have features such that, depending on a direction in which a magnetic field is applied thereto, an irreversible magnetic field strength becomes equivalent to not less than 95% of a second magnetic field strength, so that adjustment of crystal orientation thereof results in production of a superconductive material excellent in property. Further, it is useful in effecting growth of the single crystals to cause a reducing agent such as Mg and so forth to coexist at the time of the reaction, or to provide a temperature gradient in melt occurring in the course of the reaction.