Raman spectroscopic study of oxidation and phase transition in W<sub>18</sub>O<sub>49</sub> nanowires

Lu, Dongyu; Chen, J.; Zhou, Jun; Deng, Shaozhi; Xu, Ning; Xu, Jieping

doi:10.1002/jrs.1620

Cited by 87 publications

(64 citation statements)

References 21 publications

(21 reference statements)

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“…This transformation behavior matches previous studies on both W 18 O 49 and W 20 O 58 . 36,37 The laser oxidation of tungsten suboxides is a well-known phenomenon and allows us to confirm that the initial spectrum contains information about the reduced form of the NWs. The peaks we observe at low laser power cannot be indexed to a reported phase of tungsten oxide.…”

Section: Chemistry Of Materialsmentioning

confidence: 97%

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Moshofsky

Mokari

2012

Chem. Mater.

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Tungsten oxide ultrathin nanowires have potential applications in electrochromic devices, dye sensitized solar cells, gas sensors, and as photocatalysts. Herein, we report a synthesis for solution phase ultrathin nanowires with independent control over the length and diameter. W(CO) 6 is used as the tungsten source, and the solvents octadecanol and octadecene are used. Morphological control is obtained by varying the ratios between these three components as well as reaction conditions such as time and temperature. Such precise synthetic tuning will enable future investigations on the role of the aspect ratio and diameter for the above-mentioned applications. We can infer from experimental data a plausible nucleation pathway that involves the formation of tungsten alkoxide clusters. Raman spectroscopy, X-ray photoelectron spectroscopy, electron microscopy, and X-ray and electron diffraction are used to characterize the nanowires, and the results indicate the phase to be a crystallographic sheer structure, such as W 20 O 58 . ■ INTRODUCTIONTungsten oxide is perhaps most well-known for its electrochromic (EC) properties. Chromism in tungsten oxide was first demonstrated by Berzelius in 1815 by flowing hot H 2 gas over WO 3 to effect a color change. 1 However, the ability to apply an electric field to induce either transparency or visible light absorbance was demonstrated by S. K. Deb in 1969. 2 This technology is now the foundation for so-called smart windows. In spite of the large number of publications on tungsten oxide electrochromism, research is still being done to improve upon relevant properties such as coloration efficiency, stability, and coloration/bleaching time. Traditionally, the highest rates and efficiencies came from amorphous tungsten oxide films grown from vacuum deposition techniques. The drawbacks to amorphous films include their limited chemical stability and the fact that repeated ion insertion/removal degrades the films. 3 However, nanocrystalline films have recently been shown to demonstrate similar coloration efficiency and equivalent coloration times while showing greater stability. 3,4 These improvements for nanoparticle films were attributed to their large surface areas and low packing density. This rationale led to the use of vertically oriented nanowire (NW) arrays of tungsten oxide as an EC device layer and resulted in fast coloration/ bleaching times and enhanced contrast ratio between colored and bleached states. 5,6 In addition to the crystallinity and morphology, stoichiometry of the crystalline phase is an important parameter for tungsten oxide based EC device performance. It has been previously demonstrated that coloration efficiency of the substoichiometric W 20 O 58 is higher than that for WO 3 films. 7 W 18 O 49 has also been shown to exhibit good EC properties. 8 Apart from EC applications, tungsten oxide has also been shown to be useful in a number of other applications including photocatalysis, gas sensing, dye sensitized solar cells, optical recording devices, and high T ...

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Section: Chemistry Of Materialsmentioning

confidence: 97%

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Moshofsky

Mokari

2012

Chem. Mater.

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“…The O1s peak is deconvoluted into two components. The main peak at 531.3 eV and the peak observed at 533.4 eV are related to O1s in tungsten oxide and oxygen in OH-groups or a contamination [15]. The highresolution XPS spectra of W4f peaks for the other samples exhibit he same binding energies at 35.9 and 38.0 eV (not shown here).…”

Section: Characterizationmentioning

confidence: 84%

Pd2+ reduction and gasochromic properties of colloidal tungsten oxide nanoparticles synthesized by pulsed laser ablation

2012

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Tungsten oxide nanoparticles were fabricated by a pulsed laser ablation method in deionized water using the first harmonic of a Nd:YAG laser (λ = 1064 nm) at three different laser pulse energies (E1 = 160, E2 = 370 and E3 = 500 mJ/pulse), respectively. The aim is to investigate the effect of laser pulse energy on the size distribution and gasochromic property of colloidal nanoparticles. The products were characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV-Vis spectroscopy. The results indicated that WO 3 nanoparticles were formed. After ablation, a 0.2 g/l PdCl 2 solution was added to activate the solution against hydrogen gas. In this process Pd 2+ ions were reduced to deposit fine metallic Pd particles on the surface of tungsten oxide nanoparticles. The gasochromic response was measured by H 2 and O 2 gases bubbling into the produced colloidal Pd-WO 3 . The results indicate that the number of unreduced ions (Pd 2+ ) decreases with increasing laser pulse energy; therefore, for colloidal nanoparticles synthesized at the highest laser pulse energy approximately all Pd 2+ ions have been reduced. Hence, the gasochromic response for this sample is nearly reversible in all cycles, N. Tahmasebi Garavand · S.M. Mahdavi ( ) · A. Iraji zad

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“…Two strongest Raman modes at 714 and 808 cm À1 can be assigned to the W-O stretching vibrations, and four other Raman modes (86, 132, 268, and 328 cm À1 ) can be assigned to the W-O stretching vibrations of WO 3 monoclinic phase. 21,27,28 All these Raman modes, except that of the mode 86 cm À1 which showed slight changes in the relative intensity, did not have any change with the increase of operating temperature. This result indicates that the structural phase change induced by the rising of the operating temperature can be ignored in our hydrogen sensing experiments.…”

Section: Nanowire Filmmentioning

confidence: 94%

Variable-temperature Raman spectroscopic study of the hydrogen sensing mechanism in Pt-WO3 nanowire film

Luo

Chen

et al. 2013

Applied Physics Letters

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Two special properties of Pt coated WO3 (Pt-WO3) nanowire film for sensing hydrogen gas flow in air are reported in this paper, including the large relative resistance change (close to 100%) and the dependence of the millisecond-scale response time on operating temperature. A variable-temperature Raman spectroscopic system is applied to record the structural changes of WO3 nanowires in situ during the input of H2 gas at different operating temperatures. Furthermore, based on the experimental results, two combined models are proposed to be responsible for the hydrogen sensing mechanism in Pt-WO3 nanowire film.

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Raman spectroscopic study of oxidation and phase transition in W₁₈O₄₉ nanowires

Cited by 87 publications

References 21 publications

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Pd2+ reduction and gasochromic properties of colloidal tungsten oxide nanoparticles synthesized by pulsed laser ablation

Variable-temperature Raman spectroscopic study of the hydrogen sensing mechanism in Pt-WO3 nanowire film

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Raman spectroscopic study of oxidation and phase transition in W18O49 nanowires

Cited by 87 publications

References 21 publications

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Length and Diameter Control of Ultrathin Nanowires of Substoichiometric Tungsten Oxide with Insights into the Growth Mechanism

Pd2+ reduction and gasochromic properties of colloidal tungsten oxide nanoparticles synthesized by pulsed laser ablation

Variable-temperature Raman spectroscopic study of the hydrogen sensing mechanism in Pt-WO3 nanowire film

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Raman spectroscopic study of oxidation and phase transition in W₁₈O₄₉ nanowires