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.
A procedure for the Raman spectra calculation of vitreous and molten silicates was presented in this paper. It includes molecular dynamics MD simulation for the generation of equilibrium configurations, Wilson's GF matrix method for the calculations of eigenfrequencies and corresponding vectors, electro-optical parameters method (EOPM) for the Raman intensity calculations, and the bond polarizability model (BPM) for the determination of polarizability and polarizability derivative. One of the most important characteristics of this procedure is the achievement of the partial Raman spectra of five tetrahedral units, as well as the total spectral envelope. In this paper, the calculation was carried out for the vitreous and molten calcium silicates with different compositions and at various temperatures. It is worthwhile to note that the calculation is based on statistical configurations distribution in the space and so it is not needed to artificially adjust the full width at half maximum (FWHM) of spectra. It was also tested through the good agreement of the calculated spectra with the experimental, including some regularity of spectral properties. According to the calculation, the symmetrical stretching of whole tetrahedral units, to which the stretching of Si-O(nb) bond gives the main contribution to intensity, is proven to be the dominance in the high-frequency range (800-1200 cm(-1)) and the symmetrical bending of Si-O(b)-Si, to which the stretching of Si-O(b) bond exhibits the main contribution, is the dominance in the medium-frequency range (400-700 cm(-1)). As the first theoretical results, the Raman scattering coefficient of each Q(i) was found little change along with the variation of composition and temperature.
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This paper presents the characteristics of the properties of metallurgical molten slags based on the bond structure or the existence of certain ion clusters. Some experimental and theoretical approaches were adopted in the investigation. Two sets of high temperature Raman spectroscopy (HTRS) were established at Shanghai University; both can be successfully operated at 2000K or higher. One of them combines the accumulated time resolution together with the spatial resolution, and it is designed for both ultraviolet (UV) and visible (VIS) light. The SiOT model uses 5 kinds of Si‐O tetrahedra (Qn) as microsturctural units. In this model, each sample contains 250000 or more tetrahedra. The calculation using a GF matrix and electro‐optical parameter (EOP) methods were performed for every tetrahedron one by one to determine the partial Raman spectra of Qn. Then the spectra were integrated to obtain an envelope of the sample. In addition to the SiOT model, a CEMS model was also developed to link the ion cluster structure and the thermodynamic properties at equilibrium (as mixing free energy).
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