Electronic band structure of novel 18-K superconductor Y2C3 as compared with YC and YC2

The electronic band structure of yttrium sesquicarbide Y2C3(Pu2C3 structural type) reported by Akimitsu et al. (2003) as a novel 18-K superconductor is investigated using the first-principle full-potential LMTO method and compared with those of yttrium mono- and dicarbide: cubic YC and 4-K superconductor YC2 (CaC2 structural type). Our results show that the enhanced Tc of Y2C3 as compared with YC2 may be interpreted by the electronic factors: the near-Fermi DOS for Y2C3 was found to be about 70% higher that for YC2, and the contribution from the C2p states increases. The Fermi level of the "ideal" bcc Y2C3 is located near the local DOS minimum, and the superconducting properties of Y2C3-based materials would be very sensitive to synthesis conditions and the presence of impurities and lattice vacancies. We suppose that by changing these factors it is possible to vary Tc for the yttrium sesquicarbide.