Electronic and optical properties of isostructural beta-FeSi2 and OsSi2

We present both theoretical and experimental investigations of electronic and optical properties of isostructural b-FeSi2 and OsSi2 by means of a full-potential linear augmented plane wave method and optical measurements. We report also ellipsometric and reflectance measurements on samples of polycrystalline osmium disilicide prepared by mechanical alloying. From ab initio calculations these compounds are found to be indirect band-gap semiconductors with the fundamental gap of OsSi2 larger some 0.3–0.4 eV than the one of b-FeSi2. In addition to that, a low value of the oscillator strength is predicted for the first direct transitions in both cases. Computed optical functions for these materials were compared to the ones deduced from optical measurements, indicating very good agreement and the presence of some anisotropic effects.