1989 Fiscal Year Final Research Report Summary
Study of the Structure Defects and the Degradation of High-T_c Superconducting Oxide Y-Ba-Cu-O by High Resolution Electron Microscopy
| Project/Area Number |
63420046
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
Physical properties of metals
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| Research Institution | Nagaoka University of Technology |
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Principal Investigator |
NAGAKURA Sigemaro Nagaoka University of Technology, Faculty of Eng. Professor, 工学部, 教授 (80016261)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Naoki Nagaoka University of Technology, Faculty of Eng. Assistant Professor, 工学部, 助教授 (90108184)
HIROTSU Yoshihiko Nagaoka University of Technology, Faculty of Eng. Assistant Professor, 工学部, 助教授 (70016525)
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| Project Period (FY) |
1988 – 1989
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| Keywords | High-T_c Superconducting Oxide / Y-Ba-Cu-O / Bi-Sr-Ca-Cu-O / Structure Defects / Degradation by Water Vapor / High Resolution Electron Microscopy / Displacement Wave Model / Superspace Group Analysis |
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| Research Abstract |
In this research project, structures of the Y-series and Bi-series of high-T_c superconducting oxides were studied mainly by high resolution electron microscopy. The following results were obtained.
1. Study of YBa_2Cu_3O_<7-y> It was found that in crystals prepared by sintering planar defects are formed as a result of the invasion of CuO layer between BaO layers, and that the axial ratio b/a fluctuates from place to place, indicating inhomogeneous distribution of oxygen concentration. The degradation of this oxide by water vapor was also studied. The result showed that the decomposition starts at first from the separation of Ba from BaO layer and the final products are BaCO_3 formed on the specimen surface, Y(OH)_3 formed on the crystal boundary and CuO formed by the reconstruction of CuO layers.
2. Study of Bi-Sr-Ca-Cu-0 High resolution electron microscopic observations found that characteristic incommensurate modulation in the crystal is formed along the b-axis as a result of the peri
… More
odic segregation of Bi atoms and this strains the crystal severely. Based on the observation a structure model was constructed assuming displacement waves with longitudinal and transverse components. This model explained well the distribution of electron diffraction intensities. Studies were also made for crystals in which a part of Bi was replaced by Pb. The replacement was found to reduce the internal strain remarkably. A displacement wave model similar to the above explained the electron diffraction intensities. With increase of Pb a phase with longer period (incommensurate period 7b_0-8b_0; b_0 is the fundamental period) was found to appear other than the phase without Pb replacement (period 4.8b_0). When a part of Ca was replaced by Y, the incommensurate period decreases gradually with increasing amount of Y, and commensurate phases with period 4b_0 and 8b_0 are formed also. Apart from these studies an explanation of the incommensurate structure was made on the basis of superspace group theory. The superspace group N^<Bbmb> or N^<Bb2b> was derived from the extinction rule. This gave the displacement wave and the probability of atom occupancy. Comparison of the obtained results with the observed led a satisfactory result. Less
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