R. Viennois^1,2,3, L. Girard², D. Ravot², F. Terki¹, S. Charar¹, J. C. Tedenac², S. Paschen³,

A. Bentien³, F. Steglich³.

Up to now, the fundamental physical properties of CeFe₄Sb₁₂ are not well understood. For improving this knowledge, we have studied the physical properties of (Ce,La)Fe_4-xNi_xSb₁₂ by magnetic, transport and thermodynamic experiments, the substitution of La for Ce allowing us to separate the itinerant and localized magnetism. We find heavy fermion and non-Fermi liquid behaviour in CeFe₄Sb₁₂ with a high Kondo temperature. We show that the crystal electric field and the contribution of the iron should be considered. If this last contribution is stronger in LaFe₄Sb₁₂ at low temperatures, it should be very similar for both compounds at room temperature as evidenced by the thermopower experiments. Therefore, the high density of state due to a large transition metal contribution in the band structure of skutterudite is believed to be the origin of the high thermopower in (Ce,La)Fe_4-xNi_xSb₁₂. In the second part of this work, we study the thermoelectric properties of (Ce,La)Fe_4-xNi_xSb₁₂ at room temperature and notably Ce_yFe_4-xNi_xSb₁₂ with y = 4/3 – 2x/3 below 300 K. Indeed, as already show previously, these compounds are heavily doped semiconductors and therefore have the best thermoelectric properties. We find the highest power factor S²s for y @ 0,5-0,6.