Mechanisms for Tungsten Oxide Nanoparticle Formation in Solvothermal Synthesis: From Polyoxometalates to Crystalline Materials

Abstract

Understanding nucleation mechanisms of the solid state on an atomic scale is crucial in order to develop new synthesis methods for tailored materials. Here, we use in situ X-ray total scattering to follow the structural rearrangements that take place in the formation of tungsten oxide, all the way from the ionic precursor clusters in solution to the final crystalline nanoparticles. The reaction was performed in water and oleylamine to study the influence of solvent, and in both cases, the clusters present in the precursor solution adopted the well-known α-Keggin polyoxometalate structure. However, despite the similarity between precursor cluster and the final crystallographic phase, the reaction route is highly dependent on the solvent, shedding new light on nucleation mechanisms and their influence of defects in the final oxide structure. In water, the precursor cluster partly rearranges to the tungstate Y cluster before crystallization of tungsten bronze nanoparticles with a large degree of [WO6] disord...