Single crystalline and rare earth substituted La2RuO5 investigated by x-ray diffraction and EXAFS spectroscopy

Single crystals of La2RuO5 were obtained from a BaCl2 flux. The structure was determined by single crystal x-ray diffraction and compared to earlier x-ray and neutron powder diffraction results. The local structures of Ru and La/Ln in pure La2RuO5 and the rare earth substituted La2−xLnxRuO5La2−xLnxRuO5 (Ln  =Pr, Nd, Sm, Gd, Dy) polycrystalline samples were determined from the extended x-ray absorption fine structures (EXAFS) of the K- and LIII-edgesLIII-edges of Ru, La, and Ln, respectively. A four shell model was developed to reduce the number of refinable parameters in the fit of the EXAFS spectra. The distribution of the Ln-ions in the layered crystal structure was determined by a comparison of the coordination spheres obtained from the Ln-edges with the unsubstituted La2RuO5. Interatomic distances were compared to the values obtained from the single crystal diffraction and were found to agree very well.

The crystal structure of La2−xLnxRuO5La2−xLnxRuO5 (Ln=Pr, Nd, Sm, Gd, Dy) is shown viewed along the c-axis. The alternating stacking of LaRuO4 and LnO layers leads to the formation of zig-zag layers of corner sharing RuO6 octahedra. The La sites in the LaRuO4 layers are represented by light blue spheres, while the La/Ln sites in the LnO layers are colored dark blue. EXAFS investigations reveal a cationic ordering with roughly 65% of the substituting Ln ions occupying the LnO layers.Figure optionsDownload as PowerPoint slideHighlights
► Structure determination of La2RuO5 by single crystal x-ray diffraction.
► Ru-K EXAFS investigations of La2−xLnxRuO5La2−xLnxRuO5 powder samples.
► EXAFS of La and Ln   in La2−xLnxRuO5La2−xLnxRuO5 powder samples using K- and LIII-absorption edges.
► Good agreement of EXAFS results and crystal structure data despite low symmetry space group.
► Observed partial cationic ordering of the inserted Ln on the two La sites.