Collective Effect of Fe and Se To Improve the Thermoelectric Performance of Unfilled p-Type CoSb3 Skutterudites

Filled skutterudites constitute an important class of efficient and stable thermoelectric materials for power generation; however, their commercialization has been hampered due to the usage of expensive rare-earth elements as "fillers" and the nonavailability of the efficient and compatible p-type counterpart. In view of this, we report a state-of-the-art thermoelectric figure of merit (ZT) in rare-earth-free p-type unfilled CoSb3 skutterudite co-doped with Fe and Se, synthesized using a facile process of arc-melting and spark plasma sintering, which is both fast and scalable. The doping of Fe and Se have been chosen in accordance with the first-principles-based density functional theory (DFT) calculations which suggested that Fe leads to p-type conduction in CoSb3, while Se strengthens the thermoelectric properties. The experimental results also suggest that the optimized partial substitutional doping of Fe at the Co-site and Se at the Sb-site in CoSb3 leads to a favorable tuning of the electrical and thermal transport properties, which resulted in a high ZT similar to 0.7 at 870 K in an optimized skutterudite composition of Fe0.25Co0.75Sb2.965Se0.035, which is the highest value reported thus far for unfilled CoSb3-based p-type skutterudites. The resulting ZT of Fe0.25Co0.75Sb2.965Se0.035 is higher by 2 orders of magnitude than that for its pristine counterpart. In addition, the theoretically estimated transport properties of pristine and doped CoSb3, calculated employing the density functional theory (DFT) and Boltzmann transport equations, were found to be in good qualitative agreement with those measured experimentally.