University of California, Santa Cruz

We investigated the local structure of the Sb doped skutterudite CePt₄Ge_12−xSb_x using extended x-ray absorption fine structure (EXAFS) analysis. CePt₄Ge_12−xSb_x belongs to a class of materials that are currently studied for their potential thermoelectric properties. Prior analysis of CePt₄Ge₁₂ suggests that Ce may behave like a "rattler" atom in a cage, leading to a lower thermal conductivity in the material. We present a comparison of EXAFS analyses at different Sb doping levels for the Ce L_III and Pt L_III edges over a temperature range of 5-300 K. We found that the EXAFS for Ce L_III became significantly disordered with increasing Sb concentration, and for x = 3 the nearest neighbor peak (Ce-Ge) is no longer observed. The Pt nearest neighbors, however, have little disorder even at x = 3. This suggests anisotropic distortions, most likely in the plane formed by the Ce-Ge bonds and the Ge rings, which decrease the lattice thermal conductivity at low temperatures. Further research may investigate whether Sb doping pushes the rattler off-center, and more analysis at high doping levels may shed light on this material’s candidacy for thermoelectric applications.