Eur. Phys. J. B 64, 173-183 (2008)
https://doi.org/10.1140/epjb/e2008-00293-7

Strong electron-phonon coupling in Be_1-xB₂C₂: ab initio studies

Laboratoire Léon Brillouin, CEA-CNRS, UMR 0012, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

Corresponding author: ^a hamid.moudden@cea.fr

Received: 10 March 2008
Revised: 22 May 2008
Published online: 18 July 2008

Abstract

Several structures for off-stoichiometric beryllium diboride dicarbide Be_1-xB₂C₂ have been designed, and their properties studied from first-principles density functional methods. Among the most stable phases examined, the layered hexagonal structures are shown to exhibit various features in the electronic properties and in the lattice dynamics reminiscent of the superconducting magnesium diboride and alkaline earth-intercalated graphites. For substoichiometric composition x ~ 1/3, the system is found metallic with a moderately strong electron-phonon coupling through a predominant contribution arising from high frequency streching modes modulating the σ-bonding of the B–C network, and a weaker contribution at medium frequency range of the phonon spectra, arising from the intercalent motion coupled to the π-bonding states. Further, anharmonicities emerging from the proximity of the Fermi level to the σ-band edge, contributes to reduce the phonon softening hence stabilizing the structure. All these effects appear to combine favourably to produce a high temperature phonon-superconductivity.