Optimizing thermoelectric properties of filled MPt${}_4$Ge${}_{12-x}$Sb${}_x$ skutterudites by band engineering

On the basis of density functional theory (DFT) calculations thermoelectric properties are derived for Sb-doped skutterudites MPt${}_4$Ge${}_{12-x}$Sb${}_x$ with M=Ba,La,Th. It is predicted that the originally very small absolute values of Seebeck coefficients $\mathrm{\mid }S\mathrm{\mid }$ of the undoped compounds is increased by factors of 10 or more for suitable dopings. The optimal dopings correspond to a “magic” valence electron number for which all electronic states up to a (pseudo)gap are filled. The theoretical findings are corroborated by measurements of $S$ for LaPt${}_4$Ge${}_{12-x}$Sb${}_x$ skutterudites. DFT derived vibrational rattling-like modes for LaPt${}_4$Ge${}_{12}$ indicate a small value for the lattice thermal conductivity which in combination with a large value of $S^2$ makes the La-based skutterudites appear as promising thermoelectric materials.