https://scholars.lib.ntu.edu.tw/handle/123456789/177711
標題: | Hole doping into Co-12s2 copper oxides with s fluorite-structured layers between CuO2 planespiezolaminated composite plate | 作者: | Fjellvag, H. Moritaa, Y. Nagai, T. Lee, J.M. Chen, J.M. Liu, R.S. Hauback, B.C. Awana, V.P.S. Matsui, Y. Yamauchi, H. Karppinen, M. |
關鍵字: | Multi-layered copper oxides;Fluorite-structured layers;Co-12s2 homologous series;Crystal structure;Oxygen content;Hole-doping;Cu valence;XANES spectroscopy;Superconductivity | 公開日期: | 2006 | 出版社: | Taipei:National Taiwan University Dept Mech Engn | 起(迄)頁: | - | 來源出版物: | Journal of Solid State Chemistry (179),632–645 | 摘要: | In this work, the first three members (s ¼ 1, 2, 3) of the Co-12s2 homologous series of multi-layered copper oxides are gradually doped with holes through high-pressure oxygenation (HPO). The phases differ from each other only by thickness of the fluorite-structured layer block, (Ce,Y,Ca)–[O2–(Ce,Y)]s1, between two identical CuO2 planes. High-resolution transmission-electron microscopy (HRTEM) and electron diffraction (ED) analyses together with both synchrotron X-ray and neutron powder diffraction data, reveal that as a consequence of HPO the charge-reservoir CoO4-tetrahedra chains get broken and the lattice symmetry of the Co-12s2 phases changes from orthorhombic to tetragonal. Oxygen contents are analyzed for the samples with wet-chemical and thermogravimetric techniques. The valence state of copper in the CuO2 plane is determined from Cu L-edge X-ray absorption near-edge structure (XANES) spectra to be compared with the values estimated through bond-valence-sum (BVS) calculations from the crystal structure data. The positive charge induced by oxygen loading (or aliovalent CaII-for-YIII substitution in CoSr2YCu2O7+d) is found not to be completely accommodated in the CuO2 planes but be rather effectively trapped at the charge-reservoir Co atoms. Superconductivity appears in the Co-1212 (CoSr2YCu2O7+d) samples with the copper valence of 2.13 or higher, whereas in the Co-1222 (CoSr2(Ce0.25Y0.75)2Cu2O9+d) and Co- 1232 (CoSr2(Ce0.67Y0.33)3Cu2O11+d) samples Cu valence does not increase high enough to induce superconductivity. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/2006111501275479 | 其他識別: | 246246/2006111501275479 |
顯示於: | 化學系 |
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