Abstract
We have investigated the thermoelectric properties of the Ce0.9_yYbyFe4Sb12 series as well as those of a few compounds in the series Cey/2Yby/2Fe4_xCoxSb12. In the former series, increasing the Yb fraction decreases the resistivity and the Seebeck coefficient. These effects are related to the fact that Yb is not trivalent in this series. In Ce0.40Yb0.53Fe4Sb12, the phonon part of the thermal conductivity is strongly reduced compared to Ce0.85Fe4Sb12, leading to a larger figure of merit. We think that the increase of the mass and bonding fluctuations on the rare-earth site would be the main reason for this reduction. In the latter series, an extrapolated value of ZT = 0:95 at 800K was obtained in not yet optimized Ce0.44Yb0.32Fe3.02Co0.98Sb12.