Influence of Ni on the thermoelectric properties of the partially filled calcium skutterudites Ca_yCo_(4-x)Ni_xSb_(12)

摘要

We have synthesized and studied the structural and thermoelectric properties of Ni-substituted partially filled Ca_yCo_(4-x)Ni_xSb_(12) (y～0.10 and 0.18; 0 < x < 0.10) skutterudites. Electrical and thermal properties have been measured in a wide range of temperature (2-800 K). It was found that the presence of Ni increases drastically the dimensionless figure of merit at moderated temperature with respect to the Ni-free analogous samples. These greater thermoelectric properties are discussed in view of electronic structure features near E_F as resulted from KKR-CPA calculations. Both experimental findings and computed DOS characteristics point to the conclusion that another channel of electrical conductivity, related to the presence of d-Ni states and opening additional electron Fermi surface pocket, is presumably responsible for the drop of electrical resistivity with respect to the Ni-free samples. In the same time, important DOS variations near E_F were found in Ca_yCo_(4-x)Ni_xSb_(12), as previously in Ca_yCo_4Sb_(12). This gives rise to a large thermopower detected in the two series of compounds.