Structural Arrangements and Bonding Analysis of MgB₂C₂

Abstract

The orthorhombic MgB2C2 structure contains well-separated parallel graphite-like B2C2 2-layers which extend infinitely in two dimensions. Three possible ways to distribute B and C atoms in the hexagonal sublattice sites are adopted. Band structures for the hypothetical distribution patterns are examined to assess the electronic stability of these phases and to account for the observed arrangement by means of extended Hückel tight-binding calculations. The preferred choice is the layer with B and C alternating strictly so that B is nearest neighbor to C and vice versa. A rationale for this is given. Due to the alternation of B and C within the honeycomb layers, MgB2C2 is a band insulator, which through partial substitution of Mg with Li, is predicted to turn metallic with holes in the σ bands at the Fermi level.

Theoretical study of hydrogen-sorption properties of lithium and magnesium borocarbides

“…Distribution of boron and carbon atoms can be ordered (Fig. 2) [41,50], but in this case the ordering arrangement of B, C atoms in the crystal lattice is ignored. Two atoms M, B and C at once fall into the unit cell of crystal and 24 positions of H atoms are shown.…”