Fjellvag, H. and Morita, Y. and Nagai, T. and Lee, J. M. and Chen, J. M and Liu, R. S. and Hauback, B. C. and Awana, V. P. S and Matsui, Y. and Yamauchi, H. and Karppinen, M. (2006) Hole doping into Co-12s2 copper oxides with s fluorite-structured layers between CuO2 planes. Journal of Solid State Chemistry, 179. pp. 632-645. ISSN 0022-4596

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n this work, the first three members (s = 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)-[O-2-(Ce,Y)](s-1), 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 Ca-II-for-Y-III substitution in CoSr2YCu2O7+delta) 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+delta) samples with the copper valence of 2.13 or higher, whereas in the Co-1222 (CoSr2(Ce0.25Y0.75)(2)Cu2O9+delta) and Co-1232 (CoSr2(Ce0.67Y0.33)(3)Cu2O11+delta) samples Cu valence does not increase high enough to induce superconductivity.

Item Type: Article
Additional Information: Copyright for this article belongs to M/s Elsevier.
Subjects: Chemistry > Inorganic Chemistry
Chemistry > Physical Chemistry
Depositing User: Users 27 not found.
Date Deposited: 11 May 2018 05:03
Last Modified: 11 May 2018 05:03

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