Effect of partial Yb filling on thermoelectric properties of skutterudite compound RhSb3

Partially filled skutterudite compounds YbxRh4Sb12 (0 <= x <= 0.8 as nominal values) were synthesized under high pressure using a cubic anvil press. The samples were characterized by X-ray diffraction and scanning electron microscope with energy-dispersive X-ray microanalyser. Actual Yb filling ratio x of YbxRh4Sb12 increases up to 0.44, which is higher than the values for any samples prepared at ambient pressure. Thermoelectric properties of YbxRh4Sb12 were investigated in the temperature range of 2-700 K. The electrical resistivity of YbxRh4Sb12 exhibits semiconducting behavior. The resistivity decreases with increasing x. By Yb filling, the lattice thermal conductivity markedly decreases to 2.5 Wm(-1) K-1 at room temperature, from 8.2 Wm(-1) K-1 of unfilled RhSb3. The Seebeck coefficient shows a negative value (n-type conductivity). The highest dimensionless figure of merit ZT of YbxRh4Sb12 was determined to be 0.1 at 420 K for the compound with x = 0.27. The power factor is large (more than 10(-3) Wm(-1)K(-2)) over a wide temperature range between 250 and 450 K. (C) 2019 The Japan Society of Applied Physics