Intensive suppression of thermal conductivity in Nd0.6Fe2Co2Sb12-xGex through spontaneous precipitates

The best p-type skutterudites are all Fe-rich and show larger coefficient of thermal expansion than CoSb3-based n-type skutterudites, which deteriorate the reliability of thermoelectric couples constituted by p- and n-skutterudites. In this study, we synthesize Nd0.6Fe2Co2Sb12-xGex (0≤x≤1) with equal amounts of Fe and Co. Microstructure analysis reveals a unique microstructure of precipitate phases, including nanoprecipitates in skutterudite matrix, structurally imperfect nanoparticles (less than 100 nm), and unprecedented thin-layer coverings about 10 nm thick. Such rich microstructures dominate the scattering of phonons with full-length scale and remarkably suppress the lattice thermal conductivity. As a result, ZT for Nd0.6Fe2Co2Sb11.7Ge0.3 is 50% improved compared with that of a Ge free sample even with a moderately decreased power factor.