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.

Graphical abstractThe 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 full-size imageDownload 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.