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Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Bianconi, A., Congiu Castellano, A., Santis, M. D., Rudolf, P., Lagarde, P., Flank, A. M., & Marcelli, A. (1987). L2,3 XANES of the High Tc Superconductor YBa2Cu3O~7 with Variable Oxygen Content. Solid State Communications, 63(11). https://doi.org/10.1016/0038-1098(87)90650-8 Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. No evidence of Cu &3d9 final states has been found. This experiment gives direct evidence that additional oxygen x does not give Cu3+ ions with Cu 3d* configuration but gives 3d"L electronic conliguration (I.c. Cu*-Q pairs) and no gap is observed bctwccn the 3d9 (Cu+) and 3d'OL configuration (l.c. C&O-pairs). Thcrcforc in the metallic phase which exhibits superconductivitya continous set of itinerant sta~cs 3d')L and 3ti'"L is obscrvcd. In order to show that the 933 eV peak is quenched with decreasing the oxygen content x we have reduced a sample by heating it in vacuum for 2 h at 400 "C. The 933 eV peak is reduced by the heat treatment as showed in fig. 4 where the spectra of the same sample before and after the heating in vacuum are compared. The difference spectrum between the heated and not heated sample shows a clear maximum at 933 eV and this feature overlaps the high energy side of the white line. THE ELECTRONIC CONFIGURATIONThe spectra of YBa2CU306.5+x (x-0.4) and of the The difference spectrum in fig. 4 shows the lineshape of KCu(biuret)2 show a new feature at 933 eV and 933.7 eV the derivative of the white line which can be assigned to a respectively in comparison with bivalent Cu compounds. In very small energy shift of the white line induced by sample fig. 3 it is clear that in there is an reduction. This shift is in the expected direction but it is overlap between this broad feature at 933 eV and the white smaller than experimental resolution of 0.1 eV.line, while in the insulating KCu(biuret)2 compound they are In order to assign the final state configuration of the 933 completely separated by 3 eV. eV feature we have measured the spectrum of the Cu20

The Ag/MgO͑100͒ interface has been studied by EXAFS. At room temperature, in agreement with previous investigations, silver at low coverage is shown to form a two-dimensional layer at the MgO͑100͒ surface. EXAFS data demonstrate that the lattice parameter of the silver overlayer is expanded so as to fit the MgO parameter to give rise to an interface having ͑100͒ Ag ʈ(100) MgO and ͓100͔ Ag ʈ͓100͔ MgO orientation. Interface Ag atoms are atop the oxygen atoms of the MgO͑100͒ surface at a distance of 2.53Ϯ0.05 Å.

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Samples of FeCu. FeCuMn, FeCuNi, and FeCuCr alloys containing 1.5 wt% of each solute have been electron irradiated around 2 9 0 T or thermally aged Y SOOT for various times. It is known that such treatments induce Cu precipitation; the Cu depletion of the mahix is measured by the resistivity decrease of the samples. The clystallographic environment of the solute atoms in the irradiated or aged samples has been studied by %AS (x-ray absorption spemoscopy).The data show that Cr, Mn, and Ni atoms mainly remain in BCC solid solution during the CO precipitation. The first Cu precipitates are found to be of BCC structure, i.e. coherent with the matrix. At the longest ageing times, they have become of Fa' smcture. In the electronirradiated samples, the data show that, up to a Ruence of5 C cm-', most of the Cu precipitates (> 80%) are still of Bn: structure.The fraction of BCC precipitates has been estimated from both Lhe x-ray-absorption near-edge structure (XANES) and extended x-ray-absorption fine-structure (EXAFS) data It appears that, for both FeCu and FeCuMn samples, similarly aged, the FCC fraction is larger in cold-rolled samples than in pre-annealed and quenched ones.The results obtained are consistent. in the FeCu case, with a simple linear correspondence between Ruence and time, 1 C cm-' at 3 0 0 T being equivalent to -IO h at S W T . The CO precipitation is found to be accelerated, at least in its first stages, by the presence of Mn in thc alloy.

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