Thermoelectric and Transport Properties of YbzFe4−xNixSb12 Skutterudites

p -Type Yb z Fe 4− x Ni x Sb 12 (0.8 ≤ z ≤1.0, and 0.25 ≤ x ≤0.5) skutterudites were prepared, and the effects of Yb filling and Ni substitution on the thermoelectric properties were examined. X-ray diffraction patterns revealed that Yb z Fe 4− x Ni x Sb 12 skutterudites were synthesized, but small amounts of secondary phases (FeSb 2 and Sb) were produced, except for the YbFe 3.5 Ni 0.5 Sb 12 specimen. This meant that the charge compensation with Ni and the amount of Yb filling should be sufficient to stabilize the skutterudite structure. All specimens had positive Hall coefficients and Seebeck coefficients, and the carrier concentration ranged from 9.80 × 10 20 cm −3 to 3.37 × 10 21 cm −3 . The electrical conductivity decreased and the Seebeck coefficient increased with increasing Yb and Ni contents due to the decreased carrier concentration. The thermal conductivity decreased with increasing Yb and Ni contents, and YbFe 3.5 Ni 0.5 Sb 12 showed the lowest thermal conductivity. The maximum dimensionless figure of merit achieved was of 0.62 at 723 K for YbFe 3.5 Ni 0.5 Sb 12 , based on the high power factor (2.6 mWm −1 K −2 ) and the low thermal conductivity (2.9 Wm −1 K −1 ).