Electronic structure and optical properties of binary skutterudite antimonides

The electronic structure near the Fermi level of binary skutterudite antimonides and optical properties are studied by the ab initio density functional calculation method. Lattice parameters of their compounds are determined by the calculation of the total energy by taking into account the spin-orbit interaction. The calculated band structure shows that lattice parameters strongly affect the band gap and the ordering of electronic states at $\ensuremath{\Gamma}$. ${\mathrm{CoSb}}_{3}$ is a narrow gap semiconductor with the band gap ${E}_{g}=118\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. Both ${\mathrm{RhSb}}_{3}$ and ${\mathrm{IrSb}}_{3}$ are zero-gap semiconductors, where in ${\mathrm{RhSb}}_{3}$ a conduction band and a valence band overlap slightly near $\ensuremath{\Gamma}$. Band structures near the gap on binary skutterudite antimonides can be represented by the four band model consisting of the two-band nonparabolic Kane model plus two parabolic bands. By using the band model the thermoelectric power for ${\mathrm{CoSb}}_{3}$ is calculated. The obtained electronic structure and the wave function are used to calculate and discuss interband optical absorption spectra and the x-ray absorption and emission near edge structure spectra. The calculated x-ray absorption (emission) near edge structure spectra are in good agreement with recent experimental data. Also the valence band density of states is shown to describe the experimental x-ray photoelectron spectra well.