Preparation and properties of tetragonal tungsten oxyfluoride bronzes

Preparation and photoelectrolytic behavior of the systems tungsten oxide (WO3-x) and tungsten fluoride oxide (WO3-xFx)

“…Whereas the system W03_x (0 < x < 1) is monoclinic throughout the entire range,17 the system W03_xFx (0 < x < 1) undergoes the following transitions: triclinic -* monoclinic -* orthorhombic -» tetragonal -* cubic. 19,20 The structural properties of the W03_xFx prepared in this study are summarized in Table I. It can be seen that the structure remains triclinic for very small (x = 0.0079) amounts of substituted fluorine in the system W03_xFx.…”

Mechanism of Reductive Fluorination by PTFE-Decomposition Fluorocarbon Gases for WO3

“…Among the transition-metal oxides investigated so far, reductive fluorination is particularly suited for WO 3 , a material of focus in both experimental and theoretical researches. ,,− WO 3 has been found to undergo complicated structural evolutions when subjected to certain conditions. For instance, when heat is applied, the low-temperature monoclinic (II) phase transforms into a monoclinic (I) phase via a triclinic structure.…”

“…For instance, when heat is applied, the low-temperature monoclinic (II) phase transforms into a monoclinic (I) phase via a triclinic structure. The monoclinic (I) phase, which is stable at room temperature, transforms into an orthorhombic phase when heated to around 330 °C, after which it changes to a tetragonal phase. , Likewise, substituting the O 2– in WO 3 with F – has been found to form WO 3– x F x -type fluorinated WO 3 with different structural configurations depending on the amount of F. Previous studies have shown that fluorinating WO 3 using PTFE produces a WO 3– x F x whose structure changes from a monoclinic lattice to orthorhombic, tetragonal, and cubic ones with increasing degrees of fluorination. ,,− The benefits of high degrees of fluorination are represented by the cubic phase of WO 3– x F x ( x = 0.45), which manifests superconducting properties and significantly smaller resistivity compared with WO 3 and the tetragonal phase of WO 3– x F x ( x = 0.11) . The efficacy of reductive fluorination was confirmed by a study that achieved a highly fluorinated WO 3– x F x ( x = 0.60) through spark plasma sintering a mixture of WO 3 and PTFE powder, which provided photocatalytic properties .…”