Synthesis and thermoelectric properties of new partially filled CaxCo4Sb12 skutterudites

Partially filled R_xCo₄Sb₁₂ skutterudite compounds are particularly interesting for thermoelectric energy conversion at high temperature. This paper is devoted to the study of new skutterudite materials, partially filled with calcium. The Ca_xCo₄Sb₁₂ compounds (0 ≤ x ≤ 0.6, nominal) have been prepared by a conventional metallurgical route. They have been characterized by electron probe microanalysis, x-ray and neutron diffraction. The filling fraction limit was found to be x ∼ 0.2. Rietveld refinement on neutron diffraction data proved Ca atoms are inserted in the voids of the skutterudite structure. The temperature dependences of the electrical resistivity, Seebeck coefficient and thermal conductivity have been measured within the 300-800 temperature range. The influence of Ca content on the transport properties is discussed. A ZT value of 0.45 was achieved at 800 K with non-optimised Ca_0.2Co₄Sb₁₂ skutterudite.