Raman Spectroscopy of Oxide Glasses at High Pressure and High Temperature

Abstract

Multi-channel confocal micro-Raman spectroscopy was used to investigate the structure of K2Si4O9 and hydrous NaAlSi3O8 (H-Ab) glasses at high pressure (⩽15.2 GPa) and room temperature, and at ambient pressure and high temperature (⩽1246 K). The high-pressure and high-temperature data have provided insights into the structures of these glasses. For K2Si4O9 glass, the observed increase in the relative intensity of the 592 cm−1 D2 ‘defects’ band above 3.8 GPa and above Tg at 1 atm indicate that Si—O—Si linkages with small bond angles, similar to those found in three-membered rings, contribute to the D2 band. Pressure and temperature dependences of the Raman bands of K2Si4O9 glass in the 900–1200 cm−1 region indicate that a significant amount of five- and sixfold coordinated silicon atoms occurs only at P⩾7.7 GPa. Raman spectra of H-Ab glass were measured in both the low-wavenumber (100–1200 cm−1) and the O–H stretching (2700–3800 cm−1) regions. At 1 atm, the spectrum of H-Ab glass shows a broad band near 900 cm−1 and a doublet consisting of broad bands near 1000 and 1100 cm−1. The pressure and temperature dependences of the intensities of the 900 and 1000 cm−1 bands indicate that the 900, 1000 and 1100 cm−1 bands of H-Ab glass result from distorted TO4 (T=Si or Al) tetrahedra, in which the usual triple degeneracy of the antisymmetric stretching mode is lifted. In the O–H stretching region of the H-Ab glass, the presence of numerous hydrated species (e.g. OH−, H3O+ and H2O) is indicated by the splitting of the broad 3548 cm−1 asymmetric band into two bands at 2.1 GPa with peaks at 3481 and 3562 cm−1, and by their respective shifts in the negative and positive directions with increasing pressure.