Strongly reduced lattice thermal conductivity in Sn-doped rare-earth (M) filled skutterudites M CoSb Sn , promoted by Sb-Sn disordering and phase segregation.

CoSb thermoelectric skutterudite has been filled with rare-earth metals (M = La, Ce, Yb) and partially doped with Sn in specimens of M CoSb Sn stoichiometry. This has been achieved under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. A structural investigation using synchrotron X-ray diffraction data reveals a phase segregation in twin skutterudite phases with filling fraction fluctuation and different unit-cell sizes. As a result of three effects acting as phonon scatterers, namely the rattling effect of M at the wide 8 cages of the cubic 3̄ structure, the phase segregation, and the intrinsic disorder introduced by Sn substitution at the Sb sublattice, the total thermal conductivity () dramatically falls to reach minimum values under 2 W m K, well below those typically exhibited by other thermoelectric materials based upon single-filled skutterudites. The power factor is substantially enhanced to 1.11 mW m K in YbCoSbSn with respect to the unfilled composition, as a result of the charge transfer promoted by the filler.