Intermediate states ofGeO2glass under pressures up to35GPa

Abstract

Density-driven polyamorphism of $\mathrm{Ge}{\mathrm{O}}_{2}$ 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 $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and a plateau at $6--9\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. 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 $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Both the width of the FSDP and the Raman stretching band of Ge-O-Ge $(419\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$ increase with pressure but exhibit changes in behavior at 2.5 and $7.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, indicating intermediate states exist in the glass before the collapse of local tetrahedral and pentahedral structural units, respectively. At pressures above $15\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, 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 $\mathrm{Ge}{\mathrm{O}}_{2}$ glass under pressures up to $35\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.