Enhanced thermoelectric properties of Ga and In Co-added CoSb3-based skutterudites with optimized chemical composition and microstructure

Skutterudite compounds such as Co antimonite (CoSb3) contain cage-like voids inside crystal structure, which can be completely or partially filled with various different atoms, including group 13 elements. The multiple filling approach is known as an effective way of reducing lattice thermal conductivity (κlat), which results in a high value of the thermoelectric dimensionless figure of merit (zT). In this work, enhanced zT was achieved for the Ga and In co-added CoSb3 samples with a preferable microstructure and the nominal composition (Ga0.8In0.2)xCo4Sb12 (x = 0.05−0.45). Although all added In atoms occupied exclusively the void sites, the Ga species filled both the void and Sb sites of CoSb3. Moreover, Ga atoms added in the quantities exceeding the solubility limit precipitated as GaSb nanoparticles. The sample with x = 0.45 was characterized by the largest filling factions of Ga and In as well as the unique microstructure, consisting of microscale grains of the skutterudite phase and corresponding amounts of the GaSb nanoparticles. The Ga and In co-added skutterudite samples with optimized chemical composition and microstructure maintained high carrier mobility and sufficiently low κlat values, resulting in zT > 1.1, one of the best values for the skutterudites filled with group 13 elements.