Crystal chemistry and polymorphism of an iron-tungsten mixed oxide

Among the complex metal oxides, the crystal chemistry of the iron-tungsten oxide Fe2WO6 is of interest because of the existence of several crystal structures with different organizations of the FeO6 and WO6 octahedra. The conditions of polymorphism are still unclear: structures were reported in the literature for only two of the three polymorphs (α and γ) (image A) and very little is known about the third polymorph (β). In this work, our aim is to synthesize the different polymorphs of Fe2WO6 as pure products in order to be able to investigate the crystal structures and properties in more detail. We report about the synthesis procedures that we have developed starting from aqueous solutions to minimize the effects of diffusion length and maintain a homogeneous distribution of the cations during the phase formation. The stable solutions were spray-dried in order to obtain spherical particles of dried powder as small and homogeneous as possible (around 1 µm). With this technique, we were also able to control and tune the Fe/W ratio and investigate the possibility for a solid solution domain. The dried powders underwent heat treatments at various temperatures and durations before characterization by means of X-Ray Diffraction, Rietveld refinement, Scanning Electron Microscopy and 57Fe Mossbauer spectroscopy.