Thermoelectric Properties of CoSb3 Based Skutterudites Filled by Group 13 Elements

Abstract

Thermoelectric (TE) generators can directly generate electrical power from waste heat, and thus could be an important part of the solution to future power supply and sustainable energy management. The main obstacle to the widespread use of TEs in diverse industries, e.g., for exhaust heat recovery in automobiles, is the low efficiency of materials in converting heat to electricity. The conversion efficiency of TE materials is quantified by the dimensionless figure of merit, ZT, and the way to enhance ZT is to decrease the lattice thermal conductivity (κ lat) of the material, while maintaining a high electrical conductivity, i.e., to create a situation in which phonons are scattered but electrons are unaffected. Various concepts have been used in the search for this situation, e.g., the use of rattling of atoms weakly bonded in crystals and nanostructuring of materials. Here we report TE properties of skutterudites filled by group 13 elements, i.e., Ga, In, and Tl. Our group has examined the high-temperature TE properties of various skutterudites filed by group 13 elements, viz., Ga-filled CoSb3, Tl-filled CoSb3, and In/Tl double-filled CoSb3. All systems exhibit relatively high TE figure of merit, especially, Tl0.1In x Co4Sb12 achieves a dramatic reduction of κ lat, resulting in the ZT = 1.20 at 700 K—very high for a bulk material. We have demonstrated that the reduction of κ lat in Tl0.1In x Co4Sb12 is due to the effective phonon scattering both by rattling of two atoms: Tl and In and by naturally formed nano-sized In2O3 particles (<50 nm). Since the combined approach of double filling and self-formed nanostructures could be applicable to various clathrate compounds, our results suggest a new strategy in the improvement of bulk TE materials.