Theoretical study of the local structure and Raman spectra of CaO-SiO2 binary melts

Abstract

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.

The Raman coupling coefficients of calcium and sodium silicate melts in high-frequency region - SiOT model study

“…In these two modes, the stretching of O nb is along the Si-O nb bond while the stretching of O b is parallel with the line connecting both terminal Si atoms of Si-O b -Si. For a fully symmetrical tetrahedron, as depicted in our point group analysis of these five kinds of Q i -species 20 , ASS mode is of threefold degeneracy and SS mode is nondegenerate. In the previous studies 15,30 , we have pointed out that the characteristic bands for Q 2 should be not symmetrical because of the notable Raman intensities of antisymmetric stretching modes.…”

“…Following is the extending illumination of this procedure and the assessment of some parameters, and the detailed deduction and description of the formula in this procedure can be found in Ref. [15].…”

“…In the laboratory of the present authors, the HTRS technique was worked up for the microstructure study of molten silicates at the temperature up to 2000K. To facilitate the understanding of the recorded spectra, the computation of RS, VDOS and consequently corresponding CCs was progressed with a newly developed procedure 15 . This new procedure 15 is designed for the theoretical RS calculation of silicates, particularly for the glasses and melts.…”

“…All the parameters included in this potential were listed in Table 2 of Ref. 15 . Formal charges were used for each ion.…”

“…To facilitate the understanding of the recorded spectra, the computation of RS, VDOS and consequently corresponding CCs was progressed with a newly developed procedure 15 . This new procedure 15 is designed for the theoretical RS calculation of silicates, particularly for the glasses and melts. This procedure combined the classical MD simulation with Wilson's GF matrix method, electro-optical parameter method (EOPM) and bond polarizability model (BPM).…”