Quantum chemistry study on superstructure and Raman spectra of binary sodium silicates

Abstract

Raman spectra of binary sodium silicates in various components were calculated by the self-consistent field molecular orbital ab initio calculation quantum chemical (QC) method with several polysilicon-oxygen tetrahedral model clusters with both 6-31G and 6-31G(d) basis sets being applied. Relevant pure anion clusters were also be calculated in order to determine the cation effect by comparison with the available sodium series. High and intermediate Raman-active wavenumber ranges were especially considered. The symmetric stretching vibrational wavenumber of non-bridging oxygen (NBO) in the high-wavenumber range and its Raman scattering cross-section were deduced and analyzed. Several synthesized binary sodium silicate crystals were measured for comparison. The correlation between the vibrational Raman shift and the microscopic environment of the silicon-oxygen tetrahedron (SiOT) was found based on interior stress of configuration or superstructure, which depends on the connecting topology of adjacent SiOTs. A newly established empirical stress index of a tetrahedron (SIT) was introduced to elucidate the above relationship. A new notation of SiOT accompanied by superstructure information was proposed and used to describe the practical and delicate types of SiOT in various states of binary sodium silicates. The Raman scattering cross-section of the symmetric stretching vibration of NBO shows a roughly decreasing relationship with SIT or the Raman shift in the high-wavenumber range only under the circumstance of equivalent linkage between SiOTs, and Raman optical activity (ROA) enhancement ofQ 3 species occurs with Q 4 species as its nearest neighbor, which indicates the electronic coupling between them. It was also demonstrated that the Si-O b -Si bending vibrational Raman shift in the intermediate wavenumber range shows a monotonic decreasing relationship with the value of the Si-O b -Si angle while other minor impacting factors remains unknown. This work offers basic information on the superstructure of binary sodium silicates and its relationship with characteristic vibrational Raman spectra, which can be widely applied in qualitative and quantitative studies of the microstructure of silicates.

DFT‐aided interpretation of the Raman spectra of the polymorphic forms of Y2Si2O7

“…As a consequence, recently the number of ab initio studies calculating vibrational properties of silicates has been increasing continuously (e.g. Refs [11][12][13][14]). It is in this context that the polymorphism of Y 2 Si 2 O 7 becomes especially interesting, as it allows the direct comparison of structural and spectral changes within a given fixed chemistry.…”

Hydrothermal Stability of Ru/SiO2–C: A Promising Catalyst for Biomass Processing through Liquid-Phase Reactions

“…Dominant peaks at about 1340 cm −1 , 1570 cm −1 (D and G bands, respectively), 2680, and 2910 cm −1 (second-order-related features) are assigned to highly disordered carbon species [21,22], whereas the very low intensity features in the range 200-1000 cm −1 are related to structures composed of Si-O tetrahedrally coordinated units (Figure 3). Basic SiO4 building blocks (silicon-oxygen tetrahedron) connected with each other are expected to yield Raman-active modes in the range 850-1250 cm −1 (Si-O stretching), 350-500 cm −1 (O-Si-O bending), and <300 cm −1 (Si-O-Si bending, torsional/twisting, and lattice vibrations), where as amorphous silica results in a broad band spanning the 201-515 cm −1 range [23,24]. For both the SC and SC-250 samples, the low intensity features in the range of 200-1000 cm −1 could be resolved by curve fitting (Figure 4A,B) and the bands at about 467, 690, and 816 cm −1 can be associated with quartz structural fractions, whereas bands at about 290 and 400 cm −1 can be attributed to the trimidite/crystobalite polymorphs.…”

The effect of strong magnetic field on the microstructure of pure diopside and diopside doped with Fe 3+ or Mn 2+

“…The concentration of doping ions is very low in the work, and does not cause a significant variation in the Raman frequency, which is why all Raman curves are very similar to each other in Fig.4 (a). Raman intensities of these bands are relatively weak [36].…”