Polycrystalline samples of layered perovskite-related ${\mathrm{La}}_2{\mathrm{Ru}}_{1-y}{\mathrm{Mn}}_y{\mathrm{O}}_5$ ($0\le y\le 0.25$) were prepared by a soft-chemistry synthesis based on the thermal decomposition of a citrate precursor. The crystal structures of the compounds were determined by Rietveld analysis of x-ray diffraction patterns recorded at different temperatures. Additional neutron diffraction patterns for ${\mathrm{La}}_2{\mathrm{Ru}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_5$ were recorded between 1.5 K and 300 K. A structural phase transition from a monoclinic room-temperature to a triclinic low-temperature phase was observed for $y\le 0.20$, while for $y=0.25$ a phase separation at low temperatures was identified. The structural phase-transition temperatures decrease with increasing Mn concentration. Selected area electron diffraction of ${\mathrm{La}}_2{\mathrm{Ru}}_{0.75}{\mathrm{Mn}}_{0.25}{\mathrm{O}}_5$ documented the absence of cationic ordering of Ru and Mn. The Mn and Ru oxidation states were determined using x-ray absorption spectroscopy and showed a stable +4 valence for both elements in all samples investigated, at room temperature as well as at 110 K.

• Received 4 February 2014
• Revised 13 June 2014

DOI:https://doi.org/10.1103/PhysRevB.90.024406