Electronic structure properties of M${\mathrm{Si}}_2$, where M=Fe, Ru, or Os, in the orthorhombic β 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 β-${\mathrm{FeSi}}_2$ 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 β-${\mathrm{FeSi}}_2$ 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 β-${\mathrm{FeSi}}_2$. Although the theoretical lattice constant of β-${\mathrm{OsSi}}_2$ agrees well with experiment, the calculated band gap (0.06 eV) is much smaller than the band gap in β-${\mathrm{FeSi}}_2$. This strongly contrasts with experimental observations that suggest a larger band gap in β-${\mathrm{OsSi}}_2$ (1.4 – 1.8 eV). Consideration of a proposed metastable monoclinic form of ${\mathrm{OsSi}}_2$ does not remedy this discrepancy, since it is found to be a semimetal. © 1996 The American Physical Society.

• Received 9 February 1996

DOI:https://doi.org/10.1103/PhysRevB.54.7897