Structural and Dynamic Characterization of Amorphous Solids and Associated Phase Transitions. Final Report

The effect of hydrostatic pressure on the structure of glasses is not well understood. There is extensive evidence now indicating that glasses undergo structural transformation upon application of pressure. These transformations are usually evidenced by changes in density, sound velocity, and structural changes from diffraction measurements (x-ray and neutron). In vitreous GeO{sub 2}, a change in Ge-coordination from 4-6 is evidenced on the application of pressure. The coordination change reverts back to 4 on releasing the pressure indicating that the structural transformation is reversible with pressure. But a shift towards higher Q (inverse space) of the first sharp diffraction peak (FSDP) on the pressure compacted v-SiO{sub 2} and v-GeO{sub 2} suggests that application of pressure has both reversible and irreversible components such that on the release of pressure, the glass remains in a permanently compacted state