RAMAN-SPECTROSCOPY OF OXIDE GLASSES AT HIGH-PRESSURE AND HIGH-TEMPERATURE

Multi-channel confocal micro-Raman spectroscopy was used to investigat e the structure of K2Si4O9 and hydrous NaAlSi3O8 (H-Ab) glasses at hig h pressure (less than or equal to 15.2 GPa) and room temperature, and at ambient pressure and high temperature (less than or equal to 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) D-2 'defects' ban d above 3.8 GPa and above T-g at 1 atm indicate that Si-O-Si linkages with small bond angles, similar to those found in three-membered rings , contribute to the D-2 band. Pressure and temperature dependences of the Raman bands of K2Si4O9 glass in the 900-1200 cm(-1) region indicat e that a significant amount of five- and sixfold coordinated silicon a toms occurs only at P greater than or equal to 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 sp ectrum 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 usua l 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 splitti ng 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.