After the discovery of MgB2, much attention has been paid to the boride and carbide systems. In this paper, we mainly review the following themes. First, we review the present situation of the superconductivity in MgB2, which can be interpreted in terms of BCS-type phonon mediated pairing. In particular, we focus on the relationship between the superconductivity and the crystal structure in MgB2 and two gap feature. Second, we review our present status for the new superconductors including the boron and carbon systems. Recently, we discovered new superconductivity in related compounds W7Re13X (X = B and C) (Tc = 7.1 K and 7.3 K, respectively) and Y2C 3 (Tc = 18 K), and we elucidated their superconducting properties. The crystal structure of W7Re13X (X = B and C) is β-Mn type (cubic, space group: P4132), and Re atoms form a distorted octahedron. The superconductivity in W7Re13X system is recognized as strong coupling s-wave symmetry from the specific heat measurement. We discovered the superconductivity at Tc = 18 K in Y2C3, although this material with a maximum Tc of 11.5 K has already investigated by Krupka et al. The crystal structure of Y2C3 is body centered cubic (Pu2C 3-type) structure, and Y atoms are one-dimensionally aligned along  axis. The lattice parameter, a, obtained in our work is between 8.18-8.23 Å, and is smaller than those previously reported (8.21-8.25 Å).
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)