The pyrochlore solid solution (Na_0.33Ce_0.67)₂(Ir_1−xRu_x)₂O₇ (0≤x≤1), containing B‐site Ru^IV and Ir^IV 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 L_III 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.

Van der Waals assembly of two-dimensional crystals continue attract intense interest due to the prospect of designing novel materials with on-demand properties. One of the unique features of this technology is the possibility of trapping molecules between two-dimensional crystals. The trapped molecules are predicted to experience pressures as high as 1 GPa. Here we report measurements of this interfacial pressure by capturing pressure-sensitive molecules and studying their structural and conformational changes. Pressures of 1.2±0.3 GPa are found using Raman spectrometry for molecular layers of 1-nm in thickness. We further show that this pressure can induce chemical reactions, and several trapped salts are found to react with water at room temperature, leading to two-dimensional crystals of the corresponding oxides. This pressure and its effect should be taken into account in studies of van der Waals heterostructures and can also be exploited to modify materials confined at the atomic interfaces.

Solvothermal oxidation of metallic gallium in monoethanolamine for 72 h at 240 °C yields a crystalline sample of γ-Ga₂O₃ (∼30 nm crystallites). While Rietveld refinement (cubic spinel structure, Fd3̅m; a = 8.23760(9) Å) reveals that Ga occupies two pairs of octahedral and tetrahedral sites (ideal spinel and nonspinel), it provides no information about their local distribution, which cannot be statistical owing to the short Ga–Ga contacts produced if neighboring ideal spinel and nonspinel sites are simultaneously occupied. To create an atomistic model to reconcile this situation, a 6 × 6 × 6 supercell of the crystal structure is constructed and refined against neutron total scattering data using a reverse Monte Carlo (RMC) approach. This accounts well for the local as well as long-range structure and reveals significant local distortion in the octahedral sites that resembles the structure of thermodynamically stable β-Ga₂O₃. ⁷¹Ga solid-state NMR results reveal a octahedral:tetrahedral Ga ratio that is consistent with the model obtained from RMC. Nanocrystalline samples of γ-Ga₂O₃ are produced by either a short solvothermal reaction (240 °C for 11 h in diethanolamine; ∼15 nm crystallites) or by precipitation from an ethanolic solution of gallium nitrate (∼5 nm crystallites). For these samples, the Bragg scattering profile is broadened by their smaller crystallite size, consistent with transmission electron microscopy results, and analysis of the relative Bragg peak intensities provides evidence that a greater proportion of tetrahedral versus octahedral sites are filled. In contrast, neutron total scattering shows the same average Ga–O distance with decreasing particle size, consistent with ⁷¹Ga solid-state NMR results that indicate that all samples contain the same overall proportion of octahedral:tetrahedral Ga. It is postulated that increased occupation of tetrahedral sites within the smaller crystallites is balanced by an increased proportion of octahedral surface Ga sites, owing to termination by bound solvent or hydroxide.

A continuous flow reactor allows the preparation of porous metal–organic framework materials with crystallisation induced by rapid mixing of streams of preheated water and solutions of reagents in organic solvent: this gives high volume production (132 g h⁻¹) with crystallite size of the products from nanoscale to micron.