High thermoelectric figure of merit in mesostructured In0.25Co4Sb12 n-type skutterudite

Abstract The polycrystalline In 0.25 Co 4 Sb 12 n -type skutterudite was ball-milled to reduce its grain size and lattice thermal conductivity by enhanced phonon scattering at grain boundaries. To inhibit the grain size growth which occurs during the densification by spark plasma sintering, CeO 2 nanoparticles (∼20 nm) were eventually added. This leads to several highly dense In 0.25 Co 4 Sb 12 compacts (>97%) with average grain sizes ( D ) ranging from 400 nm to the very small value of 150 nm. When D ∼150 nm, the lattice thermal conductivity is strongly reduced but any improvement of the dimensionless thermoelectric figure of merit ( ZT ) is cancelled out by an obvious decrease of the electron mobility, arising from grain boundary scattering of the electrons. ZT is nonetheless improved from ZT  = 1.1 in pristine In 0.25 Co 4 Sb 12 to ZT  = 1.4 at 750 K in In 0.25 Co 4 Sb 12 with D ∼400 nm because in this sample, the lattice thermal conductivity is still efficiently reduced while the electron mobility remains unaffected.