Thermoelectric properties of La z Fe4−x Ni x Sb12 skutterudites

Abstract

p-Type La z Fe4−x Ni x Sb12 (0.8 ≤ z ≤ 1.0, 0.25 ≤ x ≤ 0.5) skutterudites were prepared, and the effects of La filling and Ni doping (charge compensation) on their transport and thermoelectric properties were examined. While X-ray diffraction analysis revealed the successful formation of the skutterudite phase, small amounts of secondary phases, including FeSb2 and Sb, were produced. However, when La and Ni contents were increased, no secondary phases were shown for the La0.9−1.0Fe3.5Ni0.5Sb12 specimen. This meant that the La filling fraction needed to be high to stabilize the skutterudite structure if the charge compensation with Ni was deficient. All samples had positive Hall coefficients and Seebeck coefficients, and the carrier concentration ranged from 8.72 × 1020 cm−3 to 2.39 × 1021 cm−3. The electrical conductivity and the thermal conductivity decreased and the Seebeck coefficient increased with increasing La and Ni contents due to the decreased carrier concentration. La0.9Fe3.5Ni0.5Sb12 achieved a maximum dimensionless figure of merit, ZT of 0.82 at 723 K on the basis of the high power factor (2.8 mWm−1K−2) and the low thermal conductivity (2.4 Wm−1K−1).