Calculated thermoelectric properties of La-filled skutterudites

Abstract

The thermoelectric properties of La-filled skutterudites are discussed from the point of view of their electronic structures. These are calculated from first principles within the local-density approximation. The electronic structure is in turn used to determine transport related quantities. Virtual-crystal calculations for La(Fe,Co)${}_{4}{\mathrm{Sb}}_{12}$ show that the system obeys near rigid band behavior with varying Co concentration, and has a substantial band gap at a position corresponding to the composition LaFe${}_{3}{\mathrm{CoSb}}_{12}.$ The valence-band maximum occurs at the $\ensuremath{\Gamma}$ point and is due to a singly degenerate dispersive band, which by itself would not be favorable for high thermopower. However, very flat transition-metal-derived bands occur in close proximity and become active as the doping level is increased, giving a nontrivial dependence of the properties on carrier concentration and explaining the favorable thermoelectric properties.