Thermoelectric and Transport Properties of Yb _z Fe_4−x Ni _x Sb₁₂ Skutterudites

Abstract

p-Type Yb _z Fe_4−x Ni _x Sb₁₂ (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 Sb₁₂ skutterudites were synthesized, but small amounts of secondary phases (FeSb₂ and Sb) were produced, except for the YbFe_3.5Ni_0.5Sb₁₂ 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 × 10²⁰ cm⁻³ to 3.37 × 10²¹ 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_3.5Ni_0.5Sb₁₂ showed the lowest thermal conductivity. The maximum dimensionless figure of merit achieved was of 0.62 at 723 K for YbFe_3.5Ni_0.5Sb₁₂, based on the high power factor (2.6 mWm⁻¹ K⁻²) and the low thermal conductivity (2.9 Wm⁻¹ K⁻¹).