Abstract
The results of a temperature-dependent, infra-red spectroscopic study of the C9, cristobalite-related phases SiO 2-cristobalite, AlPO 4-cristobalite, NaAlSiO 4-carnegieite and NaAlO 2 are presented. The effect of increasing Al substitution for Si and of Na stuffing cations are thereby investigated. Comparison of the room temperature diffuse reflectance spectra (2000-400 cm −1) shows a decrease in mean frequency in all but one of the bands with increasing Al substitution and is consistent with the increased bond length and ionic character of the Al-O bond relative to the Si-O bond. The high temperature phase transitions in each of these materials are investigated via i.r. emission spectroscopy. Dramatic changes are observed in the 550–850 cm −1region across the phase transition in each case. For SiO 2- and AlPO 4-cristobalite these changes are interpreted in terms of a Rigid Unit Mode model.
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