2006 Fiscal Year Final Research Report Summary
Improvement in Energy Conversion Efficiency of Layered Oxide Thermoelectrics Through Self-assembled Texturing
| Project/Area Number |
14103008
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| Research Category |
Grant-in-Aid for Scientific Research (S)
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| Allocation Type | Single-year Grants |
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| Research Field |
Inorganic materials/Physical properties
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| Research Institution | Nagoya University |
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Principal Investigator |
KOUMOTO Kunihito Nagoya University, Graduate School of Engineering, Professor, 大学院工学研究科, 教授 (30133094)
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| Project Period (FY) |
2002 – 2006
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| Keywords | Strontium titanate / Calcium cobaltite / Seebeck coefficient / Self-assembled texturing / Thermal conductivity / Thermoelectric figure of merit / Artificial superlattice / Natural superlattice |
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| Research Abstract |
Single crystals of homologous phase in the ZnO-In_2O_3 with layer structures were successfully grown by a flux method, and it was confirmed that the in-plane electrical conductivity is two orders of magnitude larger than cross-plane conductivity. Y-doped single crystal was found to show the in-plane conductivity similar to that of textured ceramic, and it was verified semi-quantitatively that ZT of this system would be ultimately achieved to be〜0.5.
We have succeeded in preparing high-quality epitaxial thin films of Na_<0.8>CoO_2, which further enabled us to synthesize humidity-stable Sr_xCoO_2 thin films and Na_<0.3>CoO_2・1.3H_2O exhibiting superconductivity below 4 K. We also succeeded in synthesizing epitaxial thin films of Ca_3Co_4O_9 whose thermoelectric properties are comparable to those of a bulk single crystal.
We have experimentally confirmed that the maximum ZT of heavily Nb-doped SrTiO_3 (STO) could be 0.37 at 1,000 K. In order to further improve the conversion efficiency, Eu^<2+> ions, whose ionic radius is similar to Sr^<2+>, were successfully substituted for Sr^<2+> ions to reduce thermal conductivity while maintaining the power factor without affecting the electronic transport, resulting in giving rise to the increase in ZT up to 0.39 at 1,000 K.
We found that the two-dimensional electron gas (2DEG) formed at the interface of TiO_2/SrTiO_3 exhibit giant Seebeck coefficient which is about 5 times as large as that of a bulk single crystal. We then further succeeded in fabricating the superlattices composed of undoped STO and Nb-doped STO and verified that one unit-cell layer of Nb-doped STO exhibits 4.4 times as large Seebeck coefficient as a bulk single crystal. The ZT at room temperature estimated by taking thermal conductivity of a single crystal was 2.4 which is the world record for thermoelectric energy conversion.
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[Journal Article] Oxide Thermoelectrics2006
Author(s)
K.Koumoto, I.Terasaki, T.Kajitani, M.Ohtaki, R.Funahashi
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Journal Title
in Thermoelectrics Handbook-Macro to Nano edited by D. M. Rowe, CRC Press (Taylor ＆ Francis), Boca Raton
Pages: 35-1-35-15
Description
「研究成果報告書概要(欧文)」より
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[Journal Article] Netsuden Henkan Zairyo2005
Author(s)
K.Koumoto
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Journal Title
Nihon Ceramics Kyokai, Nihon Netsuden Gakkai Hen, Kankyo Chowagata Shinzairyo Series Netsuden Henkan Zairyo, Nikkan Kogyo Shinbunsya
Pages: 43-52
Description
「研究成果報告書概要(欧文)」より
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[Journal Article] Shizen Cho Koushi Kei2005
Author(s)
K.Koumoto
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Journal Title
Nihon Ceramics Kyokai, Nihon Netsuden Gakkai Hen, Kankyo Chowagata Shinzairyo Series Netsuden Henkan Zairyo, Nikkan Kogyo Shinbunsya
Pages: 43-52
Description
「研究成果報告書概要(欧文)」より
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[Book] 熱電変換材料2005
Author(s)
河本邦仁
Total Pages
288
Publisher
日刊工業新聞社
Description
「研究成果報告書概要(和文)」より
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