The structure of permanently densified GeSe₂ glasses

GeSe₂ is an archetypal tetrahedral glass that differs from both vitreous silica and germania in that it forms a network of both edge and corner sharing tetrahedra with a substantial number of homopolar bonds at normal pressure. A combination of high energy diffraction measurements and Raman spectroscopy have been performed on glassy GeSe₂ samples with densities of 3 and 4% greater than the normal glass. The samples were pressurised in a multi-anvil cell and recovered to ambient pressure for the experiments. The higher density samples show a dramatic decrease in the first sharp diffraction peak height and shift to higher Q-values on densification. This is related to a breakdown of intermediate range order arising from the Ge-Ge interactions. X-ray difference functions suggest there is an increase in Ge-Ge corner sharing tetrahedra for the 4% denser glass compared to the normal glass. The Raman data also show a decrease in ratio of edge sharing:corner sharing tetrahedra indicating a change in the distribution of large ring structures that form the glassy network.