Search results for "Trioxide"

Low-temperature polymorphism in tungsten trioxide powders and its dependence on mechanical treatments

1999

The polymorphism of WO3 powder samples, resulting from mild mechanical treatments and from temperature changes between 30 K and room temperature, has been investigated by using Raman spectroscopy and X-ray di⁄raction. A transition from the monoclinic (I) c-phase to the triclinic d-phase after moderate mechanical treatments has been observed for untreated powder, just what happens when the same samples are rapidly cooled to low-temperature. Evidences of the low temperature monoclinic (II) polar e-phase have been found at room temperature in samples after a stronger milling treatment. The sequence of the low-temperature phase transitions appears to be strongly dependent on the mechanical hist…

Structural and vibrational study of cubic Sb2O3under high pressure

2012

We report an experimental and theoretical study of antimony oxide (Sb${}_{2}$O${}_{3}$) in its cubic phase (senarmontite) under high pressure. X-ray diffraction and Raman scattering measurements up to 18 and 25 GPa, respectively, have been complemented with ab initio total-energy and lattice-dynamics calculations. X-ray diffraction measurements do not provide evidence of a space-group symmetry change in senarmontite up to 18 GPa. However, Raman scattering measurements evidence changes in the pressure coefficients of the Raman mode frequencies at 3.5 and 10 GPa, respectively. The behavior of the Raman modes with increasing pressure up to 25 GPa is fully reproduced by the lattice-dynamics cal…

Природа центров окраски и механизм их образования в триоксиде вольфрама

1983

Photochemistry of HOSO2 and SO3 and Implications for the Production of Sulfuric Acid

2021

9 pags., 5 figs.

Atomic layer deposition of WO3 thin films using W(CO)6 and O3 precursors

2012

Here we report a new atomic layer deposition (ALD) process for WO3 thin films based on W(CO)6 as a tungsten source and ozone as a source of oxygen. A narrow ALD temperature window is found at 195–205 °C for WO3 with a deposition rate of 0.23 A per cycle. As-deposited films are partially crystalline with root mean square (rms) roughness values of 4.7 nm for 90 nm thick films; annealing the films at 600–1000 °C under oxygen or nitrogen atmospheres enhances the degree of crystallinity considerably. Our results show that the straightforward ALD chemistry of carbonyl compounds and ozone is applicable to the deposition of WO3 thin films.

XAS, XRD, AFM and Raman studies of nickel tungstate electrochromic thin films

2001

Abstract Systematic studies of nanocrystalline nickel tungstate, NiWO 4 , thin films were performed by several experimental techniques such as Ni K- and W L 1,3 -edges X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy and cyclic voltammetry measurements. We found that the NiWO 4 thin films exhibit electrochromic properties similar to that of amorphous tungsten trioxide films, but show better structural stability upon multiple colouring/bleaching cycling. It was observed that a nanocrystallinity of the thin films results in strong modifications of the NiO and WO interactions, which affect both local atomic and vibrational structures.

Sputtering deposition and characterization of Ru-doped WO3 thin films for electrochromic applications

2003

Mixed tungsten-ruthenium oxide thin films were prepared for the first time by dc magnetron co-sputtering technique and were studied by cyclic voltammetry, optical transmission measurements, Raman spectroscopy and the W L3 and Ru K edges X-ray absorption spectroscopy (XAS) in comparison with pure WO3 films. The Ru concentration was varied in the range from 0 to 28 at.%. XAS results suggest that the average local structure around both tungsten and ruthenium ions remains unchanged within experimental accuracy in all samples, moreover, for tungsten ions, it resembles that of pure WO3 films. However, the presence of the ruthenium ions affects the electrochemical and optical properties of the fil…

Tungsten oxides as catalysts in selective oxidation

1983

Abstract The reaction of allyl iodide was studied at the surface of four tungsten oxides and molybdenum trioxide. On WO2.95 and MoO3, in which crystallographic shear structures are formed on reduction, acrolein is produced at 300–400 °C, whereas W18O49 and WO2, which do not show this property, are inactive, as is WO3. It is concluded that the transformation of a corner-linked into an edge-linked arrangement of metal-oxygen octahedra provides a facile route for insertion of oxygen into a hydrocarbon molecule.

Ejection of molecules from WO3 under ion bombardment: the role of the crystal structure

1992

Abstract Emission of molecular ions from WO 3 and Na x WO 3 was studied by SIMS. It was found that the phenomenon of ejection of molecules had not arisen from specific WO bond lengths and strengths in tungsten trioxide.

Photocatalytic oxidation of trans-ferulic acid to vanillin on TiO2 and WO3-loaded TiO2 catalysts

2015

Abstract The photocatalytic oxidation of trans-ferulic acid to vanillin in water has been studied by using various TiO2 and WO3-loaded TiO2 samples as catalysts. Different values of selectivity were obtained depending on the physico-chemical properties of the single samples and a vanillin selectivity of 10% was reached in the presence of the commercial TiO2 Merck. Higher selectivity values were obtained by impregnation of TiO2 with H2WO4 followed by calcination. The increased production of vanillin exhibited by the obtained WO3-loaded TiO2 powders was attributed to a reduced further oxidation of the aldehyde caused by the presence of the practically inactive tungsten trioxide hydrate on the…