2004 Fiscal Year Final Research Report Summary
Defect Equilibrium of Perovskite-type and Related Oxides in a Thin Film or a Micro Device
| Project/Area Number |
13305046
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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 |
MIZUSAKI Junichiro Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Professor, 多元物質科学研究所, 教授 (90092345)
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| Co-Investigator(Kenkyū-buntansha) |
YASHIRO Keiji Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Research Associate, 多元物質科学研究所, 助手 (20323107)
KAWADA Tatsuya Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Associate Professor, 多元物質科学研究所, 助教授 (10271983)
MATSUMOTO Hiroshige Kyushu University, Graduate School of Engineering, Associate Professor, 大学院・工学研究院, 助教授 (70283413)
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| Project Period (FY) |
2001 – 2004
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| Keywords | defect equilibrium / perovskite / thin film / vacancy / nonstoichiometry / ionic conduction / electrochemical impedance / high temperature material |
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| Research Abstract |
1.Oxygen nonstoichiometry in a (La, Sr)CoO3 film on a (Ce, Gd)O2 substrate was investigated. Instead of using a thermogravimetry, a new electrochemical technique was developed. The electrochemical impedance was measured for the thin film using the (Ce, Gd)O2 substrate as an electrolyte. Since the rate determining step was surface reaction, the high frequency ac current measured the quantity of oxygen which is transported between the film and the electrolyte. The frequency response of the impedance gave the oxygen nonstoichiometry change. Several (La, Sr)CoO3 films of various Sr content were evaluated.. Enthalpy of oxygen vacancy formation was found to be larger for the films than for the bulk. This implies that the film shows smaller oxygen vacancy concentration than expected from the reported data for the bulk. Effect of grain size and the type of substrate on the vacancy formation enthalpy was investigated to find no clear evidence.
2.Several separate topics were investigated on the relation between microstructure and nonstoichiometry of perovskites.
(1)The reason of oxygen excess nonstoichiometry of LaMnO3 was confirmed to be the formation of cation vacancy. A sever change of microstructure was observed on the surface of LaMnO3 due to the formation and annihilation of cation vacancies.
(2)A slow cation diffusion in an n-type SrTiO3 was found to limit the cation equilibration to a thin layer around the surface. Several unique functions, such as high temperature rectification function, were found to originate from the existence of the surface layer.
(3)Microscopic fluctuation of composition in (La, Ca)(Cr, Al)O3 solid solution was found to affect its macroscopic oxygen nonstoichiometry. Quantitative representation of the oxygen nonstoichiometry was developed including the local composition fluctuation.
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