A new method of Fe2(WO4)3 preparation and its thermal stability

The title compound Fe2(WO4)3, being a metastable phase, is very difficult to prepare by a solid state synthesis route starting from the corresponding oxides. It has been prepared by a newly developed solution route starting from aqueous solutions of ferrous ammonium sulfate and sodium tungstate. The various process parameters were optimized to get a suitable precursor, which upon calcination at 500 °C for 4 h gave a well crystalline product. The product was characterized by powder XRD to have a monoclinic unit cell of Fe2(WO4)3. Its thermal stability was investigated by high-temperature XRD. It was found to decompose to FeWO4 and WO3 at 750 °C. The typical monoclinic to orthorhombic phase transition, and in turn negative thermal expansion, were not observed.