Low temperature transport and structural properties of misch-metal-filled skutterudites

Skutterudites, such as CoSb 3 , are a promising class of thermoelectric materials, particularly when the voids in the crystal structure are filled with guest atoms. We report a comprehensive study of the effects of filling skutterudites with misch-metal (Mm), a rare-earth alloy having the naturally occurring La, Ce, Pr, and Nd composition. Our power diffraction experiments show that Mm filling causes a larger expansion and an unusual distortion of the CoSb 3 lattice compared with single-element-filled skutterudites. We probed the response of crystal lattice, electronic structure, and carrier and phonon scattering mechanisms to Mm filling using neutron powder diffraction, Hall effect, electrical resistivity, thermopower, and thermal conductivity measurements between 2 and 300 K on a series of Mm y Fe 4 − x Co x Sb 12 samples. The thermoelectric properties of these Mm-filled skutterudites in this low temperature range are comparable to those of pure Ce-filled skutterudites despite the anomalous lattice expansion and distortion. We expect that these materials will have high thermoelectric figures of merit at elevated temperatures.