Electronic structure and properties of Co1-xMxSb3 (M=Fe,Ni,Pd,Pt) skutterudites

Substitution of transition metals (Fe, Ni, Pd, and Pt) for Co sites in CoSb₃ skutterudites significantly affects both the electron transport and thermal properties. For example, Fe substitution causes a large decrease in lattice thermal conductivity, and Pd or Pt substitution is suitable for optimizing the thermoelectric properties, resulting in high dimensionless thermoelectric figure of merit near 0.9. To make clear the electronic states of these transition metals and effect of substitution on the electronic structure of CoSb₃, we have systematically investigated the electronic structure of Co_1-xM_xSb₃ (M=Fe,Ni,Pd,Pt) skutterudites by x-ray photoelectron spectroscopy and inelastic electron tunneling spectroscopy. Experimental results are compared with theoretical results of band calculation made by the full-potential linearized augmented-plane-wave method. The effect of transition metal substitution on the electronic properties is discussed in terms of a model obtained from band calculations. In addition, structural defects are also discussed from the results of electron tunneling measurements. The results indicate that the substitution of transition metals for Co sites substantially affects the electronic properties of this material