Structure of Permanently Densified SiO2 Glass

SiO2 is a prototypical network-forming glass that can be processed under high pressure and temperature conditions to give a permanently densified glass with a density that is up to 23% greater than that of the pristine material. This low- to high-density amorphous transition has a profound effect on the material properties, but little is known about the accompanying structural changes and the associated mechanisms of network collapse. We will address this problem by using neutron diffraction to measure the structure of carefully chosen permanently densified SiO2 glasses. The results will be combined with those obtained from high-energy x-ray diffraction and 29Si MAS NMR to build realistic models for the structures by refining molecular dynamics configurations via the reverse Monte Carlo method. Hence, we will elucidate the mechanisms of topological change.