Syntheses of Ni-doped and Fe-doped CoSb 3 Thermoelectric Nanoparticles through Modified Polyol Process
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1166-N03-16
Syntheses of Ni-doped and Fe-doped CoSb3 Thermoelectric Nanoparticles through Modified Polyol Process Takashi Itoh1 and Keisuke Isogai1 1 EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan ABSTRACT Skutterudite CoSb3 compounds are of increasing interest as materials with good thermoelectric performance over the temperature range of 600 to 800 K, but the thermal conductivity of the materials is relatively high. Nanostructured materials have been shown to enhance phonon scattering and lower the thermal conductivity of the thermoelectric materials. Partial substitution of Ni or Fe on the Co site of CoSb3 is a hopeful route for improving thermoelectric performance of the CoSb3 compounds. In the present work, synthesis of Ni-doped and Fe-doped CoSb3 nanoparticles through the modified polyol process was attempted and the optimum synthesizing condition was investigated. Co(OOCH3)2·4H2O, Ni(OOCH3)2·4H2O, FeCl3·6H2O and SbCl3, were prepared as precursors. The precursors were reduced by NaBH4 in tetraethyleneglycol at 513 K in an argon atmosphere, for different reaction times (holding times). The reaction products were characterized by the X-ray diffraction, the energy dispersive X-ray spectroscopy, and transmission electron microscopy. The nanoparticles with about 20 to 30 nm in size mainly existed in the reaction products regardless of the chemical composition and the reaction time. The skutterudite phase was identified as a main phase in the sample synthesized for long reaction time, but the other phases of Sb and MSb2 (M=Co, Ni, Fe) were also detected. The lattice parameter of the synthesized skutterudite phase linearly increased with increasing the doping agent concentration, following Vegard’s law. INTRODUCTION More than 60 % of heat energy obtained by burning fossil fuels such as petroleum, natural gas, and coal is discharged as waste heat during energy conversion in energy systems such as automobiles, combined cycles and waste material incineration systems. Thermoelectric power generation has attracted attentions because it can directly convert the waste heat to electric energy through the thermoelectric semiconductor modules. It is expected to contribute the resolution of environmental problems and the energy security. Skutterudite compounds such as CoSb3 are well known to have the relatively good thermoelectric properties with respect to Seebeck coefficient and electrical resistivity. However, thermoelectric performance of the CoSb3 compound is not improved due to the relatively high thermal conductivity. As an approach for reduction of the lattice thermal conductivity, the crystal structure has been modified into the filled-skutterudite structure, in which the rare-earth ions are incorporated as “rattlers” into the interstitial sites of lattice [1-3]. The rattling behavior of the rare-earth ions causes phonon scattering by “guest ion”-phonon coupling [4], reducing the lattice thermal conductivity. Reduction of phonon mean free path by decreasing grain size of t
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