Physical Properties of Novel Thermoelectric Skutterudites: EuyFe4.,CoxSb12 and EuyFe4.,NixSbl2

Alloys from the two solid solutions EuyFeCxCoxSblZ and Eu~F~~.~N~~S~~~ were synthesised by argon arc-melting and isotypism was established with the skutterudite-type structure LaFe4Pl~. The Eu-content of the samples was determined by Rietveld refinements and electron microprobe measurements EMPA confirming a gradual decrease of the maximum Eucontent from y = 0.83 in EuyFe4Sblz to y = 0.44 in EuyCo4Sb12 and to y=0.56 in EuyFe2NizSblz. Eu~.~~F~~S~~~ 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 [Fe4.xCoxSb12]. To evaluate the figure of merit, thermopower, thermal conductivity and electrical resistivity measurements were performed. Due to the FeICo-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.