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

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.

[Raman spectroscopic study of silicon-oxygen tetrahedrons microstructure in x CaSiO3.LiBO2 solid solutions].

Raman spectra of xCaSiO3.LiBO2 (by weight ratio, x = 0, 0.25, 0.33, 0.50) crystals were measured. The microstructure of different silicon-oxygen tetrahedrons and their abundant variations with silica contents were studied. It shows that all the silicon-oxygen tetrahedrons are isolated by Si-Ob-B bondings or free SiO4(4-). No evidence suggests that there exist considerable Si-Ob-Si bondings. The abundance of Q2, Q4 species increases with the increasing silica content, there exists barely Q3 species even at high silica content. And the sum of integrated Raman peaks for all Qi species are linearly correlated with silica concentration in crystal, which offers the possibility to analysis silica in minerals, slags, glasses and soil samples directly.