Figure 2. Transport properties of Ce- and Yb-doped skutterudites.

The temperature dependence of: (a) electrical resistivity, (b) seebeck coefficient, (c) thermal conductivity, (e) thermoelectric figure of merit (zT) are plotted in the temperature range of 300–850 K. In figure (d) the lattice thermal conductivity with a Lorentz number of 2.0 × 10⁻⁸ V⁻² K⁻² is plotted against the filling fraction for various type of fillers. x denotes the nominal doping level of fillers. Yb_xCo₄Sb₁₂ data for x=0.20 is from Tang, Y. et al. Convergence of multivalley bands as electronic origin of high thermoelectric performance in CoSb₃ skutterudites, submitted.