Investigation of some new hydro(solvo)thermal synthesis routes to nanostructured mixed-metal oxides

We present a study of two new solvothermal synthesis approaches to mixed-metal oxide materials and structural characterisation of the products formed. The solvothermal oxidation of metallic gallium by a diethanolamine solution of iron(II) chloride at 240 °C produces a crystalline sample of a spinel-structured material, made up of nano-scale particles typically 20 nm in dimension. XANES spectroscopy at the K-edge shows that the material contains predominantly Fe2+ in an octahedral environment, but that a small amount of Fe3+ is also present. Careful analysis using transmission electron microscopy and powder neutron diffraction shows that the sample is actually a mixture of two spinel materials: predominantly (>97%) an Fe2+ phase Ga1.8Fe1.2O3.9, but with a minor impurity phase that is iron-rich. In contrast, the hydrothermal reaction of titanium bis(ammonium lactato)dihydroxide in water with increasing amounts of Sn(IV) acetate allows nanocrystalline samples of the SnO2–TiO2 solid solution to be prepared directly, as proved by powder XRD and Raman spectroscopy.