The pyrochlore solid solution (Na0.33Ce0.67)2(Ir1−xRux)2O7 (0≤x≤1), containing B-site RuIV and IrIV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O2 catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir LIII and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.

We describe a systematic study of the hydrothermal synthesis of rare-earth orthochromites, RCrO3 (R = La, Pr, Sm, Gd, Dy, Ho, Yb, and Lu) and YCrO3. All nine of these materials can be prepared in a single step by hydrothermal treatment of an amorphous mixed-metal hydroxide at temperatures above 300 °C upon heating around 24 h, with no post-synthesis annealing needed. The as-made materials are highly crystalline powders with submicrometer particle size. In the case of LaCrO3 the addition of solution additives to the hydrothermal synthesis allows some modification of crystallite form of the material, and in the presence of sodium dodecylsulfate nanocrystalline powders are produced. Profile refinement of powder X-ray diffraction (XRD) data show that each of the RCrO3 materials adopts an orthorhombic distorted (Pbmn) perovskite structure. Detailed, magnetization studies as a function of temperature reveal the high quality of the specimens, with low temperature antiferromagnetic behavior seen by direct current (DC) magnetization, and T N values that correlate with the structural distortion. A high temperature structural phase transition (∼ 540 K to rhombohedral R3̅c) seen by variable temperature XRD in the hydrothermally prepared LaCrO3 is consistent with the reported behavior of the same composition prepared using conventional high temperature synthesis.

We report a systematic investigation of orthorhombic perovskite-type RCrO 3 powder samples by Raman scattering for nine different rare earth R 3+ cations (R = Y, La, Pr, Sm, Gd, Dy, Ho, Yb, Lu). The roomtemperature Raman spectra and the associated phonon mode assignment provide reference data for structural investigation of the whole series of RCrO 3 orthochromites and phonon ab-initio calculations.The assignment of the chromite spectra and comparison with Raman data on other orthorhombic perovskites allows correlating the phonon modes with the structural distortions in the RCrO 3 series. In particular, two A g modes are identified as octahedra rotation soft modes as their positions scale linearly with the octahedra tilt angle of the CrO 6 octahedra.