2005 Fiscal Year Final Research Report Summary
Development of thermoelectric devices based on strongly correlated cobalt compounds
| Project/Area Number |
14205095
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic materials/Physical properties
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| Research Institution | Tohoku University |
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Principal Investigator |
KAJITANI Tsuyoshi Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (80134039)
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| Co-Investigator(Kenkyū-buntansha) |
MIYAZAKI Yuzuru Tohoku University, Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (40261606)
ONO Yasuhiro Tohoku University, Graduate School of Engineering, Research Associate, 大学院・工学研究科, 助手 (30211832)
GOTOH Takashi Tohoku University, Institute for Materials Research, Professor, 金属材料研究所, 教授 (60125549)
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| Project Period (FY) |
2002 – 2005
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| Keywords | Thermoelectric semiconductors / Seebeck coefficient / Thermoelectric conversion / PLD method / Electron Microscopy / Incommensurated periodicity / CDW transition / Ion-exchange method |
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| Research Abstract |
□Thermoelectric thin layered samples ;
By means of the pulsed laser deposition (PLD) technique, which was realized by the financial aid from JSPS under the present contract, following research results were obtained.
1. Smooth and well oriented La_<0.7>Ca_<0.3>MnO_3, La_<0.4>Sr_<0.6>CoO_3 and SrTiO_3 thin films with the thickness in the range from 5nm to 100nm were successfully grown by the PLD method.
2. Very smooth, e.g., the RMS of the surface roughness was about 0.5nm, thin oxide films were grown by PLD method at the optimized environment gas pressure and substrate temperature.
3. Flat and smooth La_<0.7>Ca_<0.3>MnO_3/La_<0.4>Sr_<0.6>CoO_3 multi-layer sample was grown by the PLD method and Shottky barrier height between two layers was measured. The barrier height was 0.6V, being too high for the thermionic devices.
□Following results were obtained for bulk samples ;
1. Many thin plate single crystals of Ca349 were grown by the flux-growth method. Grown single crystals have electrically co
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nducting c-planes parallel to the flat surfaces. These thin plates were carefully aligned parallel to the graphite die bottom and sintered by the spark plasma sintering (SPS) machine controlled at about 900 Celsius degree under the pressure at about 20MPa. Obtained block exhibit high thermoelectric property, i.e., ZT=0.4 at 1000K.
2. Nearly isomorphic thermoelectric bismuth-rhodium and -cobalt oxides were elucidated. Following results have been obtained. Chemical properties of both systems are quite similar.
(1)Crystal structure of thermoelectric Bi-(Sr,Ba)-Rh-O was studied by EPMA and TEM. Four or five dimensional structure model was obtained from the determined chemical contents and HREM images.
(2)Crystal structure of thermoelectric Bi-(Sr,Ca)-Rh-O was studied by EPMA and TEM. Four or five dimensional structure model was obtained from the determined chemical contents and HREM images.
(3)Thermoelectric properties of Ba, Sr or Ca substituted γ-Na_<0.7>CoO_2 samples, which were synthesized by the ion-exchange technique, were studied and their crystal structures were determined by TEM and X-ray diffraction measurement. Most of the crystals were incommensurated CDW phases. Less
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