Cationic Ordering, Solid Solution Domain, and Diffuse Reflectance in Fe₂WO₆ Polymorphs

Abstract

Single phases of the α, β, and γ polymorphs of the Fe2WO6 iron tungsten oxide were obtained through an aqueous solution route based on the combustion and heat treatment of a spray-dried precursor powder. Syntheses with Fe/W ratios ≠ 2 identified a domain of solid solutions consistent with a Fe2–2x W1+x □ x O6 scenario (x up to ∼0.025) for the defect chemistry in the temperature range around 850 °C. The crystallographic characterizations revealed a random cationic distribution in an α-PbO2-type cell for the low-temperature polymorph (α) and pointed to a reconstructive mechanism for the formation of polymorph β. A comparison of diffuse reflectance spectra confirmed the visual observation of minor color differences between the polymorphs by revealing small shifts of the absorption threshold; the Kubelka–Munk function and Tauc plots were used for comparison of the polymorphs and discussion of the results with respect to relevant literature.

Optimizing Surface Composition and Structure of FeWO4 Photoanodes for Enhanced Water Photooxidation

“…Nevertheless, the R ct value of FeWO 4 −700 °C film is 4586 Ω, which is nearly three times higher than that of the as-prepared sample. The highest charge transfer resistance from the FeWO 4 −700 °C photoanode could be originated from the presence of trace amounts of other FeWO 4 phases or minor phase segregation of iron and tungsten oxides at high postthermal temperature, [19,20] or the reduction in the conductivity of the FTO glass substrate at higher temperature. [33] The photooxidation performance of the flame-made FeWO 4 photoanodes was then studied.…”

“…While Fe 2 WO 6 has been more extensively explored, its high synthesis temperature (750-800 °C) hinders the fabrication of tunable nanostructured morphologies and its direct assembly on conventional transparent metal oxides substrates such as fluorine-doped tin oxide (FTO) or tin-doped indium oxide glass. [15][16][17][18][19][20] Conversely, FeWO 4 can be synthesized at lower temperatures by various techniques such as solvothermal, hydrothermal, and sputtering, as summarized in Table 1. Even though previous reports achieved FeWO 4 with excellent electron transport and good light absorption activity, [21][22][23][24][25] the influence of its optoelectronic and physicochemical properties on its PEC activity remains elusive.…”