Physical properties of novel thermoelectric skutterudites: Euy Fe4-xCoxSb12 and EuyFe 4-xNixSb12

Alloys from the two solid solutions Eu_yFe_4-xCo_xSb₁₂ and Eu_y Fe_4-xNi_xSb₁₂ were synthesised by argon arc-melting and isotypism was established with the skutterudite-type structure LaFe₄P₁₂. The Eu-content of the samples was determined by Rietveld refinements and electron microprobe measurements EMPA confirming a gradual decrease of the maximum Eu-content from y=0.83 in Eu_yFe₄Sb₁₂ to y=0.44 in Eu_yCo₄Sb₁₂ and to y=0.56 in Eu_y Fe₂Ni₂Sb₁₂. Eo_0.83Fe ₄Sb₁₂ orders magnetically around 84 K and the transition temperature decreases as a function of the Fe/Co and Fe/Ni substitution. X-ray absorption edge and magnetic susceptibility measurements served to define the electronic configuration of Eu and the magnetic state of the polyanions [Fe_4-xCo_xSb₁₂]. To evaluate the figure of merit, thermopower, thermal conductivity and electrical resistivity measurements were performed. Due to the Fe/Co-substitution the hole number is reduced and further compensated by the electropositive element. This influences the Seebeck coefficients significantly, which has a great impact on the figure of merit