  We show here for the first time the use of a cold sintering process (CSP) to
sinter CoSb3-based thermoelectric materials. CSP at 150 {\deg}C for 90 min
under a uniaxial pressure of 750 MPa yields pieces with a relative density of
86 %, which is increased to around 92 % after a post-annealing at temperatures
> 500 {\deg}C in Ar atmosphere. The reported CSP produces Te doped-CoSb3
nanocomposites with similar morphological and structural characteristics to the
starting nanopowders obtained by ball milling in air atmosphere. The
post-thermal treatment induces grain coalescence and grain growth, crystallite
size growth as well as compositional changes in the nanocomposite, decreasing
the amount of the main phase, CoSb3, and increasing the weight of secondary
phase, CoSb2, up to a 30 wt% at 600 {\deg}C. Remarkably, the average valence
for the Co, Sb and Te absorbing atoms is neither transformed by the sintering
process nor by the subsequent heat treatment. The functional response of the
sintered thermoelectric nanocomposites exhibits a maximum figure of merit of
0.12(3) at room temperature for the nanocomposites sintered by CSP with a
subsequent post-annealing at 500 {\deg}C. This is mainly due to its low thermal
conductivity in comparison with similar powders sintered by other approaches,
and it is explained by the morphological and structural properties. These
findings represent an attractive alternative for obtaining efficient
thermoelectric skutterudites by a scalable and cost-effective route.
