Partially filled CoSb3 skutterudite compounds are emerging materials for thermoelectric energy conversion at high temperature. CaxCo4Sb12 with different Ca contents has been prepared by the conventional metallurgical route. The temperature dependences of the electrical resistivity, Seebeck coefficient, and thermal conductivity have been measured on these compounds in the 300–800 K temperature range. These measurements have identified Ca as being a true n-type filler atom and offer, for this family of skutterudite, several valuable insights into the potential of Ca to provide good thermoelectric performance.

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We have investigated the influence of nickel doping in a series of n-type CoSb 3 skutterudite materials partially filled with Ca. The electrical resistivity, thermopower, and thermal conductivity have been measured in the 300-800 K temperature range on Ca y Co 1−x Ni x Sb 12 compounds prepared by a powder metallurgy route. The chemical composition and structure have been analyzed by electron probe microanalyses and x-ray diffraction, respectively. It was found that the presence of nickel substantially decreases the electrical resistivity without any detrimental effect on the thermopower, resulting in an improvement of the power factor. The dimensionless thermoelectric figure ZT increases with increasing temperature and reaches a maximum value of 1 at 800 K.

We have investigated the thermal and electrical properties of filled skutterudites belonging to the series Ce 1−z Yb z Fe 4 Sb 12 and Ce y/2 Yb y/2 Fe 4−x ͑Co/ Ni͒ x Sb 12 , as well as their potential for thermoelectric power generation. In the first series, increasing the Yb fraction decreases the resistivity and thermopower. These effects are related to the variations of valence of Yb with the Yb fraction ͑from 2.2 in Yb 0.92 Fe 4 Sb 12 to 2.7 in Ce 0.85 Yb 0.05 Fe 4 Sb 12 ͒. The power factor is increased in Ce 0.40 Yb 0.53 Fe 4 Sb 12 while the thermal conductivity is reduced and this leads to an improved figure of merit in this compound when compared to Ce 0.85 Fe 4 Sb 12 . Co or Ni substitution was used to tune the carrier concentration and improve the power factor: we measure a ZT = 0.5 at 500 K in Ce 0.44 Yb 0.32 Fe 3.02 Co 0.98 Sb 12 and an extrapolation leads to ZT = 0.95 at 800 K, which is close to state-of-the-art Ce 0.28 Fe 1.52 Co 2.48 Sb 12 although the composition is far from being optimized. Double filling happens to be a promising path to provide good thermoelectric performances.

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