Crystalline Tungsten Trioxide Research Articles

Enhancing Tungsten Oxide Gasochromism with Noble Metal Nanoparticles: The Importance of the Interface.

Crystalline tungsten trioxide (WO3 ) thin films covered by noble metal (gold and platinum) nanoparticles are synthesized via wet chemistry and used as optical sensors for gaseous hydrogen. Sensing performances are strongly influenced by the catalyst used, with platinum (Pt) resulting as best. Surprisingly, it is found that gold (Au) can provide remarkable sensing activity that tuned out to be strongly dependent on the nanoparticle size: devices sensitized with smaller nanoparticles display better H2 sensing performance. Computational insight based on density functional theory calculations suggested that this can be related to processes occurring specifically at the Au nanoparticle-WO3 interface (whose extent is in fact dependent on the nanoparticle size), where the hydrogen dissociative adsorption turns out to be possible. While both experiments and calculations single out Pt as better than Au for sensing, the present work reveals how an exquisitely nanoscopic effect can yield unexpected sensing performance for Au on WO3 , and how these performances can be tuned by controlling the nanoscale features of the system.

Impact of Amorphous and Crystalline Tungsten Trioxide (WO3) Thin Films as an Antireflection Material for Silicon (c-Si) Solar Cells

Impact of Amorphous and Crystalline Tungsten Trioxide (WO3) Thin Films as an Antireflection Material for Silicon (c-Si) Solar Cells

Porous nanocrystalline WO3 thin films: fabrication, electrical and optical properties

A well-designed procedure, including ion beam sputtering of aluminium (Al)–tungsten trioxide (WO3) composite films, annealing at an elevated temperature and dealloying of aluminium component, was carried out in sequence to fabricate porous nanocrystalline tungsten trioxide thin films. The texture, morphology and electrical and optical properties of the tungsten trioxide thin films were each characterised. It was found that when the annealing temperature of the aluminium–tungsten trioxide composite film reached 550°C, the obtained tungsten trioxide thin film after dealloying was nanocrystalline with a more pronounced porous structure. Electrical property tests showed that in contrast to that of amorphous tungsten trioxide films, the resistance of the porous nanocrystalline tungsten trioxide film was much greater, with a positive temperature coefficient of resistance (TCR) of +4.1 × 10−2/°C at temperatures of −10 to 5°C and a negative TCR of −2.4 × 10−2/°C at temperatures of 5 to 30°C. It was further demonstrated by ultraviolet–visible spectroscopy that compared with amorphous tungsten trioxide films, the porous crystalline tungsten trioxide film had much higher transmittance at the wavelength of visible light and a larger forbidden band width of 2.75 eV. Therefore, the porous nanocrystalline tungsten trioxide film exhibits unique or excellent electrical and optical properties, which indicate new potential applications in the fields of photoelectric devices and thermistors.

Tunable Mesoporous Structure of Crystalline WO3 Photoanode toward Efficient Visible-Light-Driven Water Oxidation

Tunable mesoporous crystalline tungsten trioxide (WO3) was synthesized by in situ surfactant-thermal-carbonization method, using the series of 2-(alkylaminomethyl)pyridine (PAL2-n, n = 8, 12, and 16) surfactant templates with varied alkyl chain length. The d-spacing, corresponding to the pore center-to-center distance, for mesoporous WO3 annealed at 550 °C decreased from 3.8 nm to 3.1 nm with a shortened chain length of PAL2-n from n = 16 to n = 12, in response to changes in the smaller size of micellar self-assemblies of PAL2-n templates. The mesoporous structure was partially collapsed for the PAL2-8 template during the crystallization of WO3 framework, when annealed at 550 °C. The longer alkyl chain of PAL2-n yielded the thicker pore walls in WO3/PAL2-n mesocomposites, affording better thermal stabilization of the organized mesoporous structure of WO3, along with the formation of higher content of carbonaceous species in mesopores through surfactant carbonization, which act as a protective support duri...

Ultrasonic disintegration of tungsten trioxide pseudomorphs after ammonium paratungstate as a route for stable aqueous sols of nanocrystalline WO3

A new facile method is proposed for the preparation of aqueous sols of highly crystalline tungsten trioxide with a particle size of 60–150 nm, containing no organic stabilizers/surfactants. These sols possess high sedimentation stability, which is quite unusual for inorganic colloidal systems containing relatively large particles, with a rather high density (ρ c(WO3) = 7.3 g/cm3). The method is based on the thermal decomposition of ammonium paratungstate, followed by dispersing the resulting powders in water under ultrasonic treatment. Thermal decomposition of ammonium paratungstate, and the composition and structure of the resulting tungsten trioxide and its aqueous dispersions, were investigated with thermal analysis combined with the mass spectrometry of gaseous thermolysis products, powder X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, IR spectroscopy and dynamic light scattering. It has been demonstrated that the high sedimentation stability of WO3 results from electrostatic stabilization, which might be caused by the formation of tungstic acid on the surface of WO3 particles when they come into contact with water. The nanocrystalline WO3 obtained can be used to produce gas sensors for ammonia.

The dependence of electrical conductivity on temperature for dry lithiated crystalline tungsten trioxide thin films

Tungsten trioxide (WO3) thin films were deposited by thermal evaporation technique and annealed at 623K for 1h. The influence of lithiation on the optical properties of the deposited films was studied. WO3 films exhibit a high optical transmittance and reduced by increasing the amount of injected lithium. The optical band gap was calculated for all the samples and it changes from 4.5 to 4eV. The electrical conductivity of different lithiated WO3 crystalized films was studied depending on temperature. The resistance behavior follows the Drude Model. This model has been verified for different amounts of lithium x. The validity of Drude model for the temperature range from 273 to 333K is fulfilled. The activation energy as well as the optical bad gap decrease as the amount of Li changes from 0.03 to 0.5. The carrier concentration as well studied.

Improvement of charge/discharge performance for lithium ion batteries with tungsten trioxide electrodes

Although a large amount of research on Li ion transportation has been carried out with the aim of improving the properties of lithium ion batteries, there has been little detailed research on electron conduction. Hence, we have been focusing on improving the charge/discharge performance of lithium ion batteries by increasing the electron conductivity of the electrodes. The electron conductivity of crystalline tungsten trioxide (WO3) was found to be increased by N2 annealing owing to the generation of oxygen vacancies. It was clarified that increasing the conductivity of the electrodes can improve the performance of lithium ion batteries, particularly their charge/discharge speed and reversibility. Additionally, the best performance was observed in a sample subjected to high-temperature annealing at 700°C in N2 ambient, which decreased the resistivity of the WO3 electrode by five orders of magnitude and simultaneously changed the monoclinic crystalline structure into a cubiclike structure into which Li ions are more easily intercalated. Therefore, to enhance the charge/discharge performance of lithium ion batteries, electron conduction should be a focus of research. Crystalline WO3 was also demonstrated to be a promising material for electrodes since oxygen vacancy generation can be induced by a simple annealing treatment, improving the electron conduction and Li ion transportation.

Selective Crystallization of W by Hydrothermal Treatment of Wastewater Containing W and Mo

Abstract Tungsten was selectively recovered from wastewater containing W and Mo, as crystalline tungsten trioxide, by hydrothermal treatment. The optimal hydrothermal conditions for selective recovery of W involved treatment at 503 K for more than 8 h after adjusting the initial pH of the wastewater to 4.

Electrochromic films with a stacked structure of WO3 nanosheets

Electrochromic films with a stacked structure of two-dimensional crystalline tungsten trioxide (WO3) nanosheets were fabricated on fluorine-doped tin oxide (FTO) coated glass by a layer-by-layer (LBL) technique. Unique electrochromic property with a slow coloration process but a fast bleaching process was observed during the insertion/extraction process of the protons into/from the stacked structure. The linear relationship between the anodic peak current density and the square root of the potential sweep rate, indicating the insertion/extraction process of the protons into/from the stacked structure is controlled by a diffusion mechanism. The nanosheet film also exhibits a coloration efficiency of 32cm2/C and an excellent long-term stability during the electrochromic process.

The anodized crystalline WO3 nanoporous network with enhanced electrochromic properties

We demonstrate that a three dimensional (3D) crystalline tungsten trioxide (WO(3)) nanoporous network, directly grown on a transparent conductive oxide (TCO) substrate, is a suitable working electrode material for high performance electrochromic devices. This nanostructure, with achievable thicknesses of up to 2 μm, is prepared at room temperature by the electrochemical anodization of a RF-sputtered tungsten film deposited on a fluoride doped tin oxide (FTO) conductive glass, under low applied anodic voltages and mild chemical dissolution conditions. For the crystalline nanoporous network with thicknesses ranging from 0.6 to 1 μm, impressive coloration efficiencies of up to 141.5 cm(2) C(-1) are achieved by applying a low coloration voltage of -0.25 V. It is also observed that there is no significant degradation of the electrochromic properties of the porous film after 2000 continuous coloration-bleaching cycles. The remarkable electrochromic characteristics of this crystalline and nanoporous WO(3) are mainly ascribed to the combination of a large surface area, facilitating increased intercalation of protons, as well as excellent continuous and directional paths for charge transfer and proton migration in the highly crystalline material.

Programming voltage reduction in phase change memory cells with tungsten trioxidebottom heating layer/electrode

A phase change memory cell with tungsten trioxide bottom heating layer/electrode isinvestigated. The crystalline tungsten trioxide heating layer promotes the temperature rise in theGe2Sb2Te5 layer which causes the reduction in the reset voltage compared to a conventional phasechange memory cell. Theoretical thermal simulation and calculation for the reset processare applied to understand the thermal effect of the tungsten trioxide heatinglayer/electrode. The improvement in thermal efficiency of the PCM cell mainly originatesfrom the low thermal conductivity of the crystalline tungsten trioxide material.

Structural and optical characterization of WO3 thin films for gas sensor applications

The structure, chemical composition, and optical properties of tungsten trioxide thin films grown by pulsed laser deposition were investigated. An ultraviolet KrF* excimer laser (λ=248nm, τFWHM≅20ns, ν=2Hz) was used for irradiation of tungsten trioxide targets in oxygen atmosphere. Our research focused on the effect of the ambient gas pressure and substrate temperature on the chemical composition, crystalline status, and optical properties of the obtained thin films. To this end, the films were studied by x-ray diffractometry Raman spectroscopy, and energy dispersive x-ray spectroscopy. Optical transmittance measurements were performed with a double beam spectrometer within the 400–1200nm range. The films deposited at oxygen pressure values higher than 10Pa and substrate temperatures above 300°C consist of crystalline tungsten trioxide. Their average transmittance in the visible-infrared spectral region reaches about 85% appropriate for the envisaged applications.