Vibrational and structural properties in the dihydrate sodium tungstate and in the dihydrate sodium molybdate crystals

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

“…This compound is composed of alternate layers of [WO 4 ] 2− tetrahedra and H 2 O in the cell with Na + presented together with the H 2 O in the layers. Two different kinds of Na + were reported according to their local coordination geometries.…”

“…Having studied Raman spectrum of NWHO, Fortes observed the bending vibrational mode of H 2 O at 1,683 cm −1 and considered that the envelope corresponding to stretching vibrational mode of H 2 O approximately at 3,300 cm −1 can be divided into four peaks (3,100, 3,297, 3,358, and 3,455 cm −1 ). Saraiva et al recorded Raman spectra of polycrystalline NWHO at low temperatures between 13 and 295 K and found that the envelope of H 2 O in the region between 3,175 and 3,450 cm −1 splits as temperature decreases, indicating the evidence of the conformational changes of the crystal. Although a basic consensus has been made on the assignment of the internal and external vibrational modes, the vibrational modes of H 2 O have not yet been clearly assigned for the crystal.…”

“…It is important to study the crystalline and molten structure of the Na 2 O–WO 3 binary system to obtain further knowledge on the temperature and pressure‐dependent phase transformation and to optimize the conditions for crystal growth from melt and then make the best preliminary assessment for the microstructure of tungstate functional crystals.…”

“…As a result, the temperature‐induced structure evolution of NWO and NWHO crystals has attracted extensive studies. After investigating the temperature‐dependent Raman spectra of NWHO from 295 to 13 K, Saraiva et al pointed out that the crystal underwent a conformational change as decreasing temperature, which was related to the arrangement of H 2 O in unit cell. Luz‐Lima et al have studied the temperature‐induced phase transformation of NWO and confirmed the presence of tilting and/or rotation of [WO 4 ] 2− tetrahedra during heating, which leads to a disorder of the [WO 4 ] 2− arrangement.…”

Joint Raman spectroscopic and quantum chemical analysis of the vibrational features of Cs2RuO4

“…Table lists all the Raman wavenumber and the damping coefficient Γ of the observed bands. All bands exhibit a rather narrow width and are located below 1000 cm −1 , which is the usual case for these kind of A 2 XO 4 (A = Na, K, Rb, Cs and X = Mo, W) compounds . Moreover, except for a change of the background shape when changing the excitation energies (from 2.41 to 1.92 eV), we did not observe any significant changes either in the intensity or in the wavenumber of these modes, confirming the non‐resonant character of the observed modes.…”