The structural and spectroscopic features of the visible light photocatalyst Bi2WO6 have been studied. Polycrystalline (PC), nanocrystalline (NC) and quantum dot (QD) sized samples were produced using solid state reaction, hydrothermal and flame spray pyrolysis methods, respectively. While the crystal structures of PC and NC are well characterized using X-ray powder diffraction data Rietveld refinement, the structural information of the QD are obtained from the complementary pair distribution function analysis and high-resolution transmission electron microscopy. The Raman spectra of the samples are compared with the phonon density of states calculated by DFT. A continuous phenomenological model describes selective optical phonon confinement into the QDs. The type of the electronic bandgaps obtained from the UV-VIS absorbance-spectra have been analyzed using two different methods, and compared with those calculated from the electronic band structures.

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Understanding material nucleation processes is crucial for the development of synthesis pathways for tailormade materials. However, we currently have little knowledge of the influence of the precursor solution structure on the formation pathway of materials. We here use in situ total scattering to show how the precursor solution structure influences which crystal structure is formed during the hydrothermal synthesis of tungsten oxides. We investigate the synthesis of tungsten oxide from the two polyoxometalate salts, ammonium metatungstate and ammonium paratungstate. In both cases, a hexagonal ammonium tungsten bronze (NH4)0.25WO3, is formed as the final product. If the precursor solution contains metatungstate clusters, this phase forms directly in the hydrothermal synthesis. However, if the paratungstate B cluster is present at the time of crystallization, a metastable intermediate phase in the form of a pyrochlore-type tungsten oxide, WO30*5H2O, initially forms. The pyrochlore structure then undergoes a phase transformation into the tungsten bronze phase. Our studies thus experimentally show that the precursor cluster structure present at the moment of crystallization directly influences the formed crystalline phase and suggest that the precursor structure just prior to crystallization can be used as a tool for targeting specific crystalline phases of interest.

Understanding material nucleation processes is crucial for the development of synthesis pathways for tailormade materials. However, we currently have little knowledge of the influence of the precursor solution structure on the formation pathway of materials. We here use in situ total scattering to show how the precursor solution structure influences which crystal structure is formed during the hydrothermal synthesis of tungsten oxides. We investigate the synthesis of tungsten oxide from the two polyoxometalate salts, ammonium metatungstate and ammonium paratungstate. In both cases, a hexagonal ammonium tungsten bronze (NH4)0.25WO3, is formed as the final product. If the precursor solution contains metatungstate clusters, this phase forms directly in the hydrothermal synthesis. However, if the paratungstate B cluster is present at the time of crystallization, a metastable intermediate phase in the form of a pyrochlore-type tungsten oxide, WO30*5H2O, initially forms. The pyrochlore structure then undergoes a phase transformation into the tungsten bronze phase. Our studies thus experimentally show that the precursor cluster structure present at the moment of crystallization directly influences the formed crystalline phase and suggest that the precursor structure just prior to crystallization can be used as a tool for targeting specific crystalline phases of interest.

High-entropy materials (HEM) represent a new class of solid solutions containing at least five different elements. Their compositional diversity makes them promising as platforms for development of functional materials. We synthesized HEMs in a complex mullite-type structure challenging previous assumptions that HEMs only form in simple structures. We present five new HEMs i.e., Bi2(Al0.25Ga0.25Fe0.25Mn0.25)4O9, and A2Mn4O10 with variations of A = Nd, Sm, Y, Er, Eu, Ce, Bi demonstrating the vast accessible composition space. By combining scattering, microscopic, and spectroscopic techniques, we show that our materials are mixed solid solutions. Remarkably, when following their crystallization in situ using X-ray diffraction and X-ray absorption spectroscopy we find that the HEMs form through a metastable amorphous phase without the formation of any crystalline intermediates. We believe that our synthetic route is excellently suited to synthesize diverse HEMs and therefore will have a significant impact on their future exploration.