Electronic structure and thermoelectric prospects of phosphide skutterudites

The prospects for high thermoelectric performance in phosphide skutterudites are investigated based on first-principles calculations. We find that stoichiometric ${\mathrm{CoP}}_3$ differs from the corresponding arsenide and antimonide in that it is metallic. As such, the band structure must be modified if high thermopowers are to be achieved. In analogy to the antimonides it is expected that this may be done by filling with La. Calculations for ${\mathrm{LaFe}}_4{\mathrm{P}}_{12}$ show that a gap can in fact be opened by La filling, but that the valence band is too light to yield reasonable p-type thermopowers at appropriate carrier densities; n-type La-filled material may be more favorable.