Color centres and polymorphism in pure WO3 and mixed (1−x)WO3−y·xReO2 powders

Abstract

Abstract.The relationship between structural transformations and colour centres creation is discussed for deeply coloured hydrogen tungsten bronzes and for pure WO3 powders, acquiring less intense colour after mechanical treatments of variable duration. A comparative study on coloration is made also for mixed compounds (1-x)WO3.y.xReO 2, where an evidence of a resonance effect for a particular Raman band at 970 cm -1, attributed to the color centres, is observed. Besides, it is found that even moderate milling treatments result in a quite different structural evolution of tungsten trioxide upon cooling.

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

“…Strong relative increase of this band, which is roughly linear vs. the Ru content, could suggest a specific resonant effect, due to the particular electronic configuration within W-O-Ru chains at the interface of the clusters. A similar evidence has been found in a former study [17,18] on polycrystalline mixtures of WO3-ReO2: a weak Raman resonance effect was detected only in the presence of ReOz, for the same W-O terminal bond vibration mode, by exciting in the red light region, and it has been attributed to the electronic configuration of the W-O-Re chain at the microcrystal interface. In that case, the surface-to-volume ratio was smaller, and the high frequency band of the terminal bonds was always lower in intensity in respect to the bulk crystal peak at 800 cm -~.…”

Raman spectroscopic study of oxidation and phase transition in W18O49 nanowires

“…The tensor for the B g modes contains nonzero xy and yz components. 13 The Raman spectrum in the low wavenumber region includes four main peaks at 87, 131, 267, and 327 cm 1 region include two peaks at 714 and 803 cm 1 , and they belong to the W-O stretching modes. 16 When the laser power is increased further from 2.3 mW to 15 mW, the phase structure of WO 3 begins to change.…”

“…12 -17 Going from room temperature to the melting point, WO 3 undergoes the phase transitions of the monoclinic ( -phase), orthorhombic (ˇ-phase) and tetragonal (˛-phase) phases in turn. 13,17 In this paper, the intrinsic Raman spectrum of W 18 O 49 nanowires was observed for the first time, and then a detailed Raman spectroscopic study on the oxidation and phase transition of W 18 O 49 nanowires with the change of laser power was carried out. EXPERIMENTAL W 18 O 49 nanowires were prepared by a high-temperature, catalyst-free, physical evaporation deposition process.…”

Influence of binder metal and surface treatment on the corrosion resistance of (W,Ti)C-based hardmetals

“…The light-blue deposit (Fig. 8) is enriched in W (Table 6) and presumably is WO 3 formed by oxidation of the W at high corrosion potentials [10,45]. The porosity of the light-blue oxide layer might be associated with binder phase depletion.…”