Electronic structure of Si and Ge gold-doped clathrates

Abstract

The electronic properties of single phase type-I clathrate compounds, ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}(\mathrm{Si}\mathrm{}or\mathrm{}\mathrm{Ge}{)}_{40}$ and ${\mathrm{Ba}}_{8}{\mathrm{Ge}}_{46\ensuremath{-}x}$ have been investigated. The crystal structure, electrical resistivities, magnetic susceptibilities, the density of states at the Fermi level, and the band gap (where applicable) were determined. ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}{\mathrm{Si}}_{40}$ and ${\mathrm{Ba}}_{8}{\mathrm{Au}}_{6}{\mathrm{Ge}}_{40}$ show a metallic behavior whereas ${\mathrm{Ba}}_{8}{\mathrm{Ge}}_{46\ensuremath{-}x}$ is semiconducting. On a basis of this work, a first evidence is presented of the existence of type-I mixed-clathrates containing both silicon and germanium.