1995 Fiscal Year Final Research Report Summary
Observation of Oxygen Vacancies in Perovskite Oxide by a 200kV HREM
| Project/Area Number |
06805002
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | KYOTO UNIVERSITY OF EDUCATION |
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Principal Investigator |
SHIBAHARA Hiroyasu Kyoto University of Education, Associate Professor, 教育学部, 助教授 (60144408)
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| Project Period (FY) |
1994 – 1995
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| Keywords | HREM / Oxygen-vacancies / Perovskite / IMAGE PROCESSING / DEFECTIVE-STRUCTURE |
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| Research Abstract |
The perovskites with the general formula XYO_3 have been extensively studied because of their interesting ferroelectric ad magnetic properties. The systems of LaMnO_<3-X> and BaMnO_<3-X> consist of a staking of close-packed layrs of LaO_3/BaO_3 with Mn metals occupying interlayr octahedral site. Analyzes of their oxygen-defective structures are of interest because of the magnetic properties depending on the content of oxygen vacancy. Establishment of imaging condition of a HREM for reflecting oxygen-defective structure is of importance. The structural determination and quantification of oxygen vacancies in LaMnO_<3-X> were carried out in 200/300kV HREM equipped with an imaging plate. On the basis of direct observation with HREM and the aid of computer simulation and image processing, optimum imaging conditions were found, where oxygen atoms and the vacancies are imaged as bright spots in a "dark-spot image". Under the optimum imaging conditions, the dependence of image contrast on the atomic occupancies of the oxygen sites and the thickness of the samples was discussed on the basis of dynamical diffraction theory. By an imaging plate, the atomic occupancies were quantitatively estimated from the intensity distributions of the bright spots in the observed image contrast. Using the relaxd structure derived from molecular dynamics simulation, image contrast based on the multi-slice method could assist the understanding of the observed image contrast by HREM.Besides, as an application of structural determination by the present method, hydroxyapatite in tooth crystals was studied to ascertain the positions of the OH^- groups.
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