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

n-type skutterudites Co0.97Pd0.03Sb3 + nano-CeO2 and Co0.94Ni0.06Sb3 + nano-CeO2 nanocomposites were synthesized by ball milling and spark plasma sintering in order to promote phonon scattering at the grain boundaries. Addition of nano-CeO2 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 Co0.97Pd0.03Sb3 + 2% CeO2 and Co0.94Ni0.06Sb3 + 3% CeO2. 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 Co0.94Ni0.06Sb3 + 3% CeO2, an improved ZT (∼0.7) is obtained at 700 K. Annealing Co0.97Pd0.03Sb3 + 2% CeO2 at 825 K leads to a slightly increased grain size (240 nm), which remains stable on a long term (95 days).