Vibrational properties of silicates: A cluster model able to reproduce the effect of “SiO4” polymerization on Raman intensities

Abstract

An ensemble of ten silicate clusters is examined using quantum chemical calculations (Density Functional Theory) as a potential model to study the effect of polymerization of the SiO 4 units on Raman intensities of silicates (crystalline and amorphous). Quite originally, instead of saturating non-bridging oxygen (NBO) with hydrogen atoms as generally found in the literature for similar approaches, NBOs, which hold a negative charge if not saturated, have been substituted by isoelectronic fluorines whose mass is corrected in normal mode calculations to be equal to that of an oxygen. By adjusting the number of fluorines per silicon, the different Q n coordination types characterizing the different classes of silicates are modeled. The relevance of this ensemble of clusters as a model to study the effect of polymerization on Raman intensities is established in several steps, the most important one being the qualitative reproduction of evolution of the Ip polymerization index with the number of bridging oxygen per silicon.

Raman spectroscopic investigations of natural jennite from Maroldsweisach, Bavaria, Germany

“…The center peak originates from Si–O–Si bending and corresponds well with the calculated position of 655 cm −1 . Symmetric stretching vibrations of Q 1 chain‐end Si–tetrahedra are responsible for the peak at 906 cm −1 . The presence of this peak confirms the presumption of the presence of subparallel fibers.…”

“…Measurements of a perfect single crystal should not give a peak at that wavenumber, because chain‐end Si‐tetrahedra will not be present in central parts of the crystal. The Raman bands between 950 and 1015 cm −1 can be assigned to symmetric stretching of Q 2 sites . The band at 1000 cm −1 shows a strong dependence on orientation, in contrast to the two bands at 969 and 986 cm −1 (Fig.…”

The Raman signature of protonic species as a potential tool for dating or authentication of glazed pottery

“…The representative Raman spectra obtained from the glazes of the pottery samples are given in Figure . All spectra display the characteristic Raman signature of a silicate type of glass: two broad features at about 450 and 1,000 cm −1 , which represent the Si–O bending and stretching modes, respectively . For the porcelain glazes with silica‐rich composition that have a high melting temperature (approximately 1350–1400 °C), the bending mode band is much stronger than the stretching one (Figure a,b,d,e) .…”

“…[34,39,[42][43][44][45][46] The different components of the Si-O stretching bands arise from the different population of the SiO 4 tetrahedra in the form of isolated and more or less connected arrangements. It has been pointed out both experimentally [45,46] and by modelling [47] that the area ratio of bending to stretching band is directly related to the degree of polymerization of the SiO 4 vibrational (and chemical) unit and hence to the melting temperature of glass. The representative Raman spectra obtained from the glazes of the pottery samples are given in Figure 6.…”

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

“…Properly chosen small model structures have often been successfully applied in the literature for characterization of the main vibrational properties in crystalline and non‐crystalline systems . Such models work well in cases when the main moiety of the compound interacts only weakly with the surroundings.…”