The structure of pressure-compacted vitreous germania

Neutron diffraction measurements have been performed on normal and pressure-compacted vitreous GeO2 using the LAD spectrometer at the ISIS spallation pulsed neutron source and the SLAD diffractometer at NFL Studsvik. Four cylindrical GeO2 samples, which had been subjected to pressures between 0 (ambient pressure) and 6 GPa, were studied. The first peak of the diffraction pattern shifts to higher scattering vector magnitude, Q, with increasing density (preparation pressure), indicating a modification of the medium range order resulting from a compaction of the network cages. The real space correlation function, T(r), shows that the mean Ge–O bond length only changes very slightly for glasses prepared at pressures up to 6 GPa, inferring that GeO6 octahedra are not present in significant numbers in the glass following pressure release. However changes in the first Ge–Ge peak with increasing density indicate a progressive reduction of the mean Ge–Ô–Ge bond angle.