Raman studies of Al coordination in silica-rich sodium aluminosilicate glasses and some related minerals (original) (raw)

Journal of Non-Crystalline Solids, 1984

Abstract

ABSTRACT Polarized Raman spectra have been obtained for a series of sodium aluminosilicate glasses and selected minerals, in order to investigate changes in the glass structure with composition. Particular attention is paid to characterization of the Al coordination, and to test Lacy's hypothesis concerning the role of “triclusters” in Al-rich glasses (Al/Na = R > 1.0). A comparison of five glasses ranging from nearly sodium trisilicate composition glass (R = 0.03) to albite composition glass (R = 1), and beyond to a glass of R = 1.61, leads to the following observations with increasing R: the polarized bands previously assigned to T-O (non-bridging) vibrations (950, 1110 cm−1) decrease in intensity, while those assigned to T-O (bridging) vibrations (485, 980 cm−1) either remain the same or increase in intensity. The narrow band at 495 cm−1 and a somewhat wider one at 595 cm−1, may be related to Raman active “defects” that have been observed in vitreous SiO2 at essentially the same frequencies. Our observations indicate a general increase in tetrahedral polymerization and random incorporation of Al into tetrahedral sites. Comparison of the Raman spectra of mullite (which contains (Si, Al)3O10 triclusters) with sillimanite (which contains no triclusters) shows that the bands at 418 and 1200 cm−1 in mullite are absent for sillimanite. Assuming that these “extra” bands are due to the triclusters in mullite, we have to conclude that similar triclusters do not exist in any of the glasses we examined. If these “extra” bands in mullite are not due to triclusters, we can draw no such conclusion. Our study indicates that observed changes in physical properties of sodium aluminosilicate glasses as R increases are not due to an Al coordination change.

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