A polycrystalline phase of Hf-filled CoSb3 skutterudite was successfully prepared by the mechanical alloying technique followed by the spark plasma sintering process. X-ray diffraction and scanning electron microscopy linked with energy-dispersive x-ray spectroscopy were used to investigate the result filling the void spaces with Hf. HfCo4Sb12 skutterudite possesses a very low thermal conductivity [1.8 W/(m K)], lower than that of some lanthanide-filled skutterudites, while exhibiting p-type conduction. The anharmonicity of oscillation of the loosely bond Hf atoms, the point defects on the lattice microstructure and the large area fraction of the grain boundaries were the reasons for the significant drop in the thermal conductivity of Hf-filled CoSb3. Thus, this work is useful in deriving a pathway for improvement in thermoelectrics through the introduction of smaller rattling cations with higher mass to increase the disorder of the lattice structure.
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