Fe, Ru, and Os disilicides: Electronic structure of ordered compounds.

Abstract

Electronic structure properties of {ital M}Si{sub 2}, where {ital M}=Fe, Ru, or Os, in the orthorhombic {beta} phase are investigated using the linear muffin-tin orbital method in the atomic sphere approximation. Selective substitution of Fe with Ru, Os, and Cr in {beta}-FeSi{sub 2} is also studied. These compounds are small-gap semiconductors with theoretical energy band gaps ranging from 0.06 to 0.50 eV, with the exception of the metallic Cr-substituted disilicides. Substitution of Ru or Os for Fe in {beta}-FeSi{sub 2} leads to a reduction of the gap width, an increase in volume of the unit cell, and a bulk modulus similar to or slightly smaller than for {beta}-FeSi{sub 2}. Although the theoretical lattice constant of {beta}-OsSi{sub 2} agrees well with experiment, the calculated band gap (0.06 eV) is much smaller than the band gap in {beta}-FeSi{sub 2}. This strongly contrasts with experimental observations that suggest a larger band gap in {beta}-OsSi{sub 2} (1.4 {endash} 1.8 eV). Consideration of a proposed metastable monoclinic form of OsSi{sub 2} does not remedy this discrepancy, since it is found to be a semimetal. {copyright} {ital 1996 The American Physical Society.}