BONDING IN THE MOLYBDENUM SILICIDES

Full-potential linear muffin-tin orbital calculations are reported for the bulk properties, density of states, and electron density in A2 Mo , A15 Mo3Si, D8(m) Mo5Si3, C11(b) MoSi2, and A4 Si. Both the magnitude and the directional anisotropy of the valence charge density associat ed with bonds in the three silicides suggest a hierarchy in bond stren gth, ordered from strongest to weakest: Mo-Mo, Mo-Si, and Si-Si. A com bined Mulliken and tight-binding analysis shows this behavior to coinc ide with variations in occupation of the respective types of bonding s tates, which is ultimately traced to Mo(Bd) site energies that are nea rly degenerate with the Fermi level, in contrast to Si(3p) site energi es lying about 5 eV higher. These characteristics point to the dominan ce of Mo-Si bonding in C11(b) MoSi2, consistent with the near pd hybri dization gap in this material, which appears to explain the unique pos ition of the disilicide in systematics of the molybdenum silicide bulk properties. Finally, having identified the critical elements of the e lectronic structure in the molybdenum silicides, this work provides a physically motivated basis upon which to improve models used in the st udy of large-scale Mo-Si interface problems.