In-situ studies on the micro-structure evolution of A 2 W 2 O 7 (A = Li, Na, K) during melting by high temperature Raman spectroscopy and density functional theory

You

et al. 2021

J Raman Spectroscopy

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Comparing with the crystalline tungstate compounds, little work has been carried out and reported on the relation among the microstructure, W–O bond lengths, and characteristic Raman‐active vibration wavenumber of the molten tungstates, which allows us to diagnose and determine the structure of unknown clusters existing in and further predict the physicochemical properties of molten binary alkali tungstates. Raman spectra of an ensemble of eight model clusters were simulated in the present work by density functional theory (DFT) to establish the effect of the fine structures and W–Onb (non‐bridging oxygen) bond lengths of W–O complexes on the characteristic wavenumber of W–Onb Raman‐active vibration modes of the molten tungstates. Results show that the characteristic wavenumbers of the symmetric stretching vibration modes of W–Onb bonds increase almost linearly with the decreasing bond length. The characteristic wavenumbers of W–Onb symmetric stretching vibration modes generally follow [WO4]2− > [WO5]4− > [WO6]6− present in the melt simultaneously. The characteristic wavenumbers were also found to increase with the number of bridging oxygen for the same W–O complex. In situ Raman spectra of molten A2WnO3n + 1 (A = Li, Na, K; n = 1, 2, 3) were then measured in order to verify the correlation observed among the microstructure, W–O bond lengths, and characteristic Raman‐active vibration mode wavenumbers. The correlation was successfully applied to deconvolute the in situ Raman spectrum of the molten Na2W3O10.

Section: Resultssupporting

confidence: 60%

Q_{1}^{1}

), [ 23,24,29 ] and [W 3 O 10 ] 2− trimer (

2 Q_{1}^{2}

and

Q_{2}^{11}

), [ 30–32 ] respectively, for n values of 1, 2, and 3. This is consistent with the trend shown in Figure 2, namely, v ( Q 0 ) < v (

Q_{1}^{1}

) < v (

Q_{1}^{2}

) < v (

Q_{2}^{11}

).…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fine structures and their impacts on the characteristic Raman spectra of molten binary alkali tungstates

You

et al. 2021

J Raman Spectroscopy

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“…Previous studies have demonstrated that Raman scattering spectroscopy is a feasible and informative tool for investigating the phase transformation of tungstates and probing the structure of W–O complexes in crystalline, glassy, and molten states. The relative intensities show the variation in the relative amount of each species.…”

Section: Introductionmentioning

confidence: 99%

In‐situ high‐temperature Raman spectroscopic studies of the vibrational characteristics and microstructure evolution of sodium tungstate dihydrate crystal during heating and melting

You

et al. 2018

J Raman Spectroscopy

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In-situ studies of the vibrational characteristics and microstructure evolution of the Na 2 WO 4 ·2H 2 O (sodium tungstate dihydrate) crystal during the temperature-induced solid-state phase transformation and melting process were carried out using high-temperature Raman spectroscopic technique. Results showed that the thermal decomposition process of the Na 2 WO 4 ·2H 2 O crystal takes place mainly within the temperature range of 348-383 K, along with the structure transforming from the orthorhombic to cubic symmetry. As the sample temperature increased further, another solid-state phase transformation from the cubic to orthorhombic structure was observed approximately at 893 K before melting occurred at 1023 K. Although the isolated [WO 4 ] 2− tetrahedron was preserved within the entire temperature range from room temperature to 1023 K, subtle changes were observed with the mean bond length of W-O bonds in the tetrahedron unit. Furthermore, Raman active vibrational modes of Na 2 WO 4 ·2H 2 O, two Na 2 WO 4 crystal phases, and corresponding melt were assigned based on the density functional theory simulation and compared with the literature data. Finally, four-molecule cluster arranged as T d symmetry is considered to be the most likely configuration in the molten state according to density functional theory simulation based on the different multimolecular clusters proposed.

“…The in situ HTRS and DFT methods further improved the structure information of W–O complexes in the crystal, melt, and solid–liquid phase transitions, which is beneficial to the optimization of the conditions of crystal growth from melt for tungstate functional crystals. 145 Furthermore, they investigated the Raman spectra of sodium disilicate crystal, glass, and its melt structure. The Raman spectra of Na 2 Si 2 O 5 from room temperature to 1773 K was measured in solid and liquid states, and the temperature-dependent variations of the structure units were analyzed.…”

Section: Introductionmentioning

confidence: 99%

A Review of Chinese Raman Spectroscopy Research Over the Past Twenty Years

et al. 2019

This paper introduces the major Chinese research groups in the fields of biomedicine, food safety, environmental testing, material research, archaeological and cultural relics, gem identification, forensic science, and other research areas of Raman spectroscopy and combined methods spanning the two decades from 1997 to 2017. Briefly summarized are the research directions and contents of the major Chinese Raman spectroscopy research groups, giving researchers engaged in Raman spectroscopy research a more comprehensive understanding of the state of Chinese Raman spectroscopy research and future development trends to further develop Raman spectroscopy and its applications.