Intermediate states of GeO₂ glass under pressures up to 35 GPa

Density-driven polyamorphism of GeO₂ glass under high pressure has been studied by density, x-ray scattering, and optical Raman measurements. Density data obtained by an x-ray absorption method display distinct compression behavior in different pressure regions, with rapid density increases at 5 and 10 GPa and a plateau at 6–9 GPa. Simultaneous x-ray diffraction reveals that the position of the first sharp diffraction peak (FSDP) increases nearly linearly towards higher scattering vector with pressure up to 10 GPa. Both the width of the FSDP and the Raman stretching band of Ge-O-Ge (419 cm⁻¹) increase with pressure but exhibit changes in behavior at 2.5 and 7.5 GPa, indicating intermediate states exist in the glass before the collapse of local tetrahedral and pentahedral structural units, respectively. At pressures above 15 GPa, post-octahedral compression with progressive enhancement in network correlation is observed. The results indicate not only the discrete but also rotating intermediate states exist in GeO₂ glass under pressures up to 35 GPa.