Synthesis and thermoelectric properties of Sb0.20CoSb2.80 skutterudite

Polycrystalline samples of cobalt antimonide (CoSb2.79) were submitted to different conditions of pressure, temperature and processing time, in a high-pressure toroidal-type chamber, aiming to maximize the production of the high pressure phase previously observed in experiments with a diamond anvil cell. Rietveld refinements of X-ray powder diffraction data were performed to determine the phase composition and structural parameters. The maximum yield, 89(2) wt.% of SbxCoSb3−x phase, was obtained at 7.7 GPa, 550 °C and (at least) 5 min of processing time. The mechanism behind the formation of SbxCoSb3−x at high pressure and high temperature is actually not the same as that previously inferred from experiments at higher pressures (20 GPa) and room temperature with the diamond anvil cell. Indeed, evidences suggest that, at high pressure and high temperature, SbxCoSb3−x is formed by insertion of Sb resulting from decomposition of cobalt antimonide. Thermal conductivity, Seebeck coefficient and electrical conductivity were estimated for CoSb2.79 and Sb0.20CoSb2.80. The thermoelectric figure of merit at room temperature for Sb0.20CoSb2.80 resulted 33% greater than that for CoSb2.79.