Thermoelectric Properties of Carbon Nanotubes Added n-type CoSb 3 Compound
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Thermoelectric Properties of Carbon Nanotubes Added n-type CoSb3 Compound Takashi Itoh1, Masashi Tachikawa2 1 EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan 2 Department of Materials, Physics and Energy Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan ABSTRACT Cobalt triantimonide compounds are well known as materials with good thermoelectric properties over temperature range of 550-900 K. For further improving thermoelectric performance, reduction of thermal conductivity is required. In this study, we attempted to disperse carbon nanotubes (CNTs) homogeneously into the n-type CoSb3 compound for lowering lattice thermal conductivity by the phonon scattering. Powders of Co, Ni, Sb and Te were blended with molar ratios of n-type Co0.92Ni0.08Sb2.96Te0.04 compound, and the compound was synthesized through a pulse discharge sintering (PDS) process. After coarsely grinding the synthesized compound, CNTs were mixed with the compound powder at different mass% (0, 0.01, 0.05 and 0.1 mass%). Then, the mixture was mechanically ground with a planetary ball milling equipment. The ground composite powder was compacted and sintered by PDS. Thermoelectric properties (Seebeck coefficient, electrical resistivity and thermal conductivity) of the sintered samples were measured. It was confirmed that the fibrous CNTs existed homogeneously in the compound matrix. The absolute value of Seebeck coefficient slightly decreased with increase of CNT content. The minimum thermal conductivity was obtained at addition of 0.01mass%CNT, and the electrical resistivity was a little increased with CNT content. The maximum ZT of 0.98 was achieved at 853 K in the 0.01mass%CNT-added sample. INTRODUCTION More than 60 % of heat energy generated from various energy systems such as automobiles, combined cycles and waste material incineration systems is discharged as waste. The thermoelectric power generation that directly converts heat energy to electric energy through the thermoelectric semiconductor elements has received considerable attention and is expected to contribute to the resolution of environmental problems and energy security. High-performance thermoelectric semiconductors are required for a high conversion efficiency in power generation. 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. In our previous works[5, 6], the nano-size particles o
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