Evidence of fivefold-coordinated Ge atoms in amorphous GeO2 under pressure using inelastic x-ray scattering
Résumé
Elucidating pressure-induced structural transitions in glasses at a microscopic level is a formidable challenge. Here, the local environment of amorphous germania (a-GeO2) is investigated, from room pressure up to 18 GPa, using in situ inelastic x-ray-scattering measurements at the oxygen K-edge. The appearance of GeO5 units at intermediate pressures, a debated yet unsolved issue in the literature, is probed experimentally and their amount quantified. It is found that these units are minority species at all the pressures investigated, discarding the previously proposed fully pentacoordinated glassy state. The presence of GeO5 units, which occur as transient species as the glass undergoes a transition from the tetrahedral to octahedral Ge-coordination states, provides a microscopic basis for the understanding of glass behavior at intermediate pressures.