Transport Property in the Filled Skutterudite Structure

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Researches on thermoelectric semiconductors with high efficiency to convert heat energy to electric energy are expected to solve modern problems such as sufficient supply of clean energy, waste heat recovery, and development of micro electron techniques. The compound of the RFe_4Sb_<12> system (R=rare earth element) with the filled skutterudite structure is a candidate for the next thermoelectric semiconductor, because it possesses both very large mobility of charge carriers and many scattering centers of phonons.This research investigated the filled skutterudite structure, the thermoelectric property, the transport mechanisms of charges carriers and phonons in the compound of the RFe_8Sb_<24> system (R=rare earth element) by means of X-ray diffraction experiments, transmission electron microscopic observations, EDX analyses, measurement of the Seebeck coefficient, electrical resistivity, thermal conductivity, moessbauer effect and the Hall coefficient.The filled skutterudite structure exists with various compositions in a limited range of valence electron total number 142-144 in a unit cell. The filling number of rare earth element in voids increases with decreasing the number of the forth element on Fe sites. The lattice parameter and the shape of Sb ring depend on the Ce filling number in voids. The Seebeck coefficient depends on valence electron total number per unit volume. By adding the forth element, or by controlling the filling number of rare earth element in voids, the electrical resistivity, the thermal conductivity, the carrier density, the hole mobility, the scattering frequency of phonons can be changed in order to get good power factor, the good figure of merit.