Mesostructured thermoelectric Co1−yMySb3 (M = Ni, Pd) skutterudites

Abstract n-type skutterudites Co 0.97 Pd 0.03 Sb 3  + nano-CeO 2 and Co 0.94 Ni 0.06 Sb 3  + nano-CeO 2 nanocomposites were synthesized by ball milling and spark plasma sintering in order to promote phonon scattering at the grain boundaries. Addition of nano-CeO 2 slows down the grain size growth of the skutterudite matrix which occurs during sintering, leading to grain sizes as small as respectively 220 and 170 nm in Co 0.97 Pd 0.03 Sb 3  + 2% CeO 2 and Co 0.94 Ni 0.06 Sb 3  + 3% CeO 2 . Subsequently, the lattice thermal conductivity is reduced by up to 47% at 300 K. An experimental value of ∼110 nm can be estimated for the bulk phonon mean free path in both compounds. In Co 0.94 Ni 0.06 Sb 3  + 3% CeO 2 , an improved ZT (∼0.7) is obtained at 700 K. Annealing Co 0.97 Pd 0.03 Sb 3  + 2% CeO 2 at 825 K leads to a slightly increased grain size (240 nm), which remains stable on a long term (95 days).