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Enhancement of Electrical Properties of the Thermoelectric Compound Ca3Co4O9 through Use of Large-grained Powder

Published online by Cambridge University Press:  03 March 2011

Masashi Mikami*
Affiliation:
National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan; and Japan Science and Technology Agency, CREST, Kawaguchi, Saitama 332-0012, Japan
Emmanuel Guilmeau
Affiliation:
National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan; and Japan Science and Technology Agency, CREST, Kawaguchi, Saitama 332-0012, Japan
Ryoji Funahashi
Affiliation:
National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan; and Japan Science and Technology Agency, CREST, Kawaguchi, Saitama 332-0012, Japan
Kangji Chong
Affiliation:
Osaka Electro-Communication University, Neyagawa, Osaka 572-0833, Japan
Damiel Chateigner
Affiliation:
CRISMAT-ENSICAEN Laboratory, UMR CNRS 6508, 14050 Cean Cedex, France
*
a) Address all correspondence to this author. e-mail: m-mikami@aist.go.jp
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Abstract

Hot-forged Ca3Co4O9 (Co349) ceramics were synthesized using large-grained powders prepared by a flux-growth method, and their thermoelectric properties and degree of grain alignment were evaluated. Neutron-diffraction experiments evidenced the effect of grain size on the development of the c-axis grain alignment. The optimum grain size was around 7 μm in our hot-forging method. The electrical resistivity (ρ) in the direction parallel to the pressed-plane was more reduced at higher degrees of orientation. Since ρ was reduced without lowering the Seebeck coefficient (S), the power factor (PF = S2/ρ) of the Co349 sample was improved and reached 0.8 mW/mK2 at 1073 K using Co349 grains with average size of around 7 μm. The thermal conductivity (κ) in the direction parallel to the pressed-plane slightly increased with the increase of the grain size, however the improvement of PF owing to use of large-grained powder outweighed this negative impact on the κ component of the thermoelectric figure of merit (Z = S2/ρκ).

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Articles
Copyright
Copyright © Materials Research Society 2005

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References

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