Revisiting the five-decade-old structure of the Fe₂WO₆ powder with incommensurate modulations

Iron tungstate, Fe₂WO₆, is a promising photocatalytic, thermoelectric and electrochemically active material for energy storage devices. However, its structure is poorly described in the literature reporting on these applications. For the first time, we solved the crystal structure of its high temperature form using powder X-ray diffraction and the incommensurately modulated structural model. The structure adopts a (3 + 1)-dimensional Pbcn(0β0)000 superspace group with the cell parameters a = 4.57964(7) Å, b = 5.58662(8) Å, and c = 4.96920(7) Å and the modulation vector q = 0.6687(4) b*, close to the commensurate case q = 2/3 b*. The first-order satellite reflections visible in the powder diffraction patterns show, compared to the main reflections, a substantial broadening of the diffraction lines, caused by the small size of the ordered domains. This broadening has been successfully described using a line-broadening model, designed for incommensurately modulated structures, and confirms the incommensurate structural description. Such findings can be of great help to further understand the reported physical and electrochemical properties.