Abstract
The structural changes and densification mechanisms of silica glass with compression up to 15GPa at 300 degrees centigrade has been investigated by infra-red absorption and X-ray diffraction measurement. The density increases with apllied pressure. But the rate of increase changed between 7.5GPa and 10GPa. It may suggest that are two the densification mechanisms change at this pressure range. Infra-red spectra of densified silica glass showed a systematic shift of the high frequency bands (nu=~1100cm-1) and a remarkable decrease in the intensity of the low frequency bands (nu=~470cm-1). They can be attributed to a decrease in Si-O-Si angle and possibly to an existence of high coordinated silicon. Structures of these densified silica glass have been analyzed based on the radial distribution function curves (RDF(r)) derived from the X-ray scattering intensities. It showed almost no pressure variations in atomic distances and angles, coordination number. However, the intensity of FSDP (First Sharp Diffraction Peak), whichi is attributed to the intermediate range structure of the glass (ring structure of the glass), decreases to 10GPa. It may indicate increase in a number of non-bridging oxygen. And linear change in the FSDP position with increasing pressure provides evidence for increase of small ring structure (three or four memberd rings of SiO4 tetrahedra).
