Crystal chemistry and magnetism of iron-tungsten mixed oxide

Iron tungstate Fe2WO6 attracts interest due to its photoelectrochemical and magnetic properties. On the one hand, Fe2WO6 is studied either as a photocatalyst for degradation of environmental pollutants [1,2] or as a photoanode for water oxidation in tandem devices [3-4]. On the other hand, some magneto-dielectric properties [5] have been reported, confirming that further work is needed to investigate the magnetic and electric properties. Indeed, Fe2WO6 iron tungstate exists as three crystal structures with different organizations of the FeO6 and WO6 octahedra [6-8].
In the present work, we have clarified the conditions of polymorphism using a complete set of the three polymorphs as single-phase products. In particular, a spray-drying route from aqueous solution had to be developed for the synthesis of the low temperature α polymorph. We have revised the structural model for this α-polymorph, solved the heretofore-unknown structure of the β-polymorph and compared magnetic properties through bulk magnetic measurements and preliminary neutron diffraction results. We also report on the influence of the Fe/W ratio using a combination of X-Ray diffraction, 57Fe Mossbauer spectroscopy, scanning electron microscopy and ICP-OES quantification.