The ''Realstruktur'' of the system La2-xSrxCu1-yRuyO4-delta studied by rietveld and extended X-ray absorption fine structure spectroscopy

The structure of the layered perovskite-related system La2-xSrxCu1-yRuyO4-delta was investigated by Rietveld refinement calculations of X-ray diffraction data and EXAFS analysis of the Ru-K and Cu-K absorption edge, Both methods complement one another as they yield information about long-range ordering and the local environment of a specific element, respectively. Rietveld calculations have revealed remarkable changes of the interatomic distances with the composition, e.g., the degree of elongation of the Cu/Ru-O-6 octahedra. To get more detailed information about the local structure vie have performed EXAFS studies for selected samples with y = 0, 0.2, 0.4, 0.6, 0.8, and 1. We were able to achieve consistent results both from the Ru-K and Cu-K edge data. As an element specific method, extended X-ray absorption fine structure (EXAFS) spectroscopy is capable of distinguishing between different possible arrangements of the La/Sr and Cu/Ru atoms. We found that La and Sr are distributed statistically on the A cation position. For the B cations a small enrichment of Cu in the Ru surrounding (and vice versa) could be detected, For a given value of y this enrichment increases with increasing La content, This indicates a partial ordering of Ru and Cu within the perovskite layers. Oxygen vacancies (delta > 0) were found to be located exclusively in the Cu surrounding. Coordination numbers less than 5 reveal that a part of the copper ions is coordinated in a square planar way, Distances derived from EXAFS and XRD data show a good agreement; still, the former are usually smaller by 0.01-0.03 Angstrom. The distance Cu-La/Sr was found to be smaller by 0.05 Angstrom than the distance Ru-La/Sr. Apart from this, no significant differences could be detected for the distances between the various combinations of elements.