Physical properties of novel thermoelectric skutterudites: Eu/sub y/Fe/sub 4-x/Co/sub x/Sb/sub 12/ and Eu/sub y/Fe/sub 4-x/Ni/sub x/Sb/sub 12/

Alloys from the two solid solutions Eu/sub y/Fe/sub 4-x/Co/sub x/Sb/sub 12/ and Eu/sub y/Fe/sub 4-x/Ni/sub x/Sb/sub 12/ were synthesised by argon arc-melting and isotypism was established with the skutterudite-type structure LaFe/sub 4/P/sub 12/. 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/sub y/Fe/sub 4/Sb/sub 12/ to y=0.44 in Eu/sub y/Co/sub 4/Sb/sub 12/ and to y=0.56 in Eu/sub y/Fe/sub 2/Ni/sub 2/Sb/sub 12/. Eo/sub 0.83/Fe/sub 4/Sb/sub 12/ 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/sub 4-x/Co/sub x/Sb/sub 12/]. 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.