Thermoelectric properties and electronic structure of Sn- and Te-doped CoSb3 skutterudites

Thermoelectric properties and electronic structure of Sn- and Te-doped CoSb₃ skutterudites

J. Tobola¹, K. Wojciechowski², J. Ciellak¹, J. Leszczylski²

^{1Faculty of Physics and Nuclear Techniques, AGH University of Science and Technology,
Al. Mickiewicza 30, 30-059 Cracow, Poland
^{2Faculty of Materials Science and Ceramics, AGH University of Science and Technology,
Al. Mickiewicza 30, 30-059 Cracow, Poland}}

Electron transport properties of Sn- and Te-doped CoSb₃ skutterudites were studied by electrical resistivity, thermopower, Hall effect and thermal conductivity measurements. The crystal structure of powder samples was analyzed by the Rietveld refinements of X-ray diffraction data. ¹¹⁹Sn Mossbauer technique was used for investigations of Sn atom distributions. It was shown that the obtained spectra could be fitted by two sets of hyperfine parameters related to different Sn positions.

Electronic structure of both ordered compounds (XCo₃Sb₁₂, X= Sn, Sb, Te, vacancy) and disordered alloys (CoSb_3-xX_x, X=Sn, Te, vacancy) were calculated by the charge self-consistent KKR-CPA methods. This approach allowed determining density of states (DOS) of impurities placed in the semiconducting CoSb₃.

It was noticed that in doped CoSb₃ the Fermi level fell either into the edge of valence (Sn impurity) or conduction (Te impurity) band. Such DOS features remained in line with type of carriers detected from the thermopower results. Moreover, the KKR-CPA showed that Sn and Te doping should lead to more “metallic" properties with respect to the pure CoSb₃. Such trends were observed on resistivity curves in most doped samples On the other hand, the computations showed that more complex behaviors could be expected if various defects appeared.