This research used resources of the APS, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. GeoSoilEnviroCARS is supported by NSF Earth Sciences Grant EAR-1128799) and Department of Energy (DOE) GeoSciences Grant DE-FG02-94ER14466. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. Petitgirard for providing preliminary EOS data for SiO 2 glass. GCS is the alliance of the three national supercomputing centers, Höchstleistungsrechenzentrum Stuttgart (Universität Stuttgart), JSC (Forschungszentrum Jülich), and Leibniz-Rechenzentrum (Bayerische Akademie der Wissenschaften), funded by the German Federal Ministry of Education and Research and the German State Ministries for Research of Baden-Württemberg, Bayern, and Nordrhein-Westfalen.
We thank the Gauss Center for Supercomputing (GCS) for providing computing time for a GCS Large Scale Project on the GCS share of the supercomputer JUQUEEN ( 51) at Jülich Supercomputing Center (JSC). These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si–O coordination. Si–O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. We show that SiO 2 first undergoes a change in Si–O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We investigated the structure of SiO 2 glass up to 172 GPa using high-energy X-ray diffraction.
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