Variable Range Hopping transport in narrow-gap semiconducting partially filled skutterudites

Physical properties of the Ce_yFe_4-xNi_xSb₁₂ filled skutterudite solid solution are studied with nominal compositions following y = (4 - 2x)/3. Low temperature experiments confirmed that these compounds are heavily doped narrow-gap semiconductors. We notably observe a semiconducting-metal transition at about 150 K for y ≥ 0.6 and a type Mott Variable Range Hopping transport behaviour at lower temperature for 0 < y < 1. Finally, for 0.6 ≤ y ≤ 0.8, when T > 650 K, we observed optimized thermoelectric properties equivalent to the ones of the state-of- the-art materials