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  • Title: Beyond sixfold coordinated Si in SiO2 glass at ultrahigh pressures.
    Author: Prescher C, Prakapenka VB, Stefanski J, Jahn S, Skinner LB, Wang Y.
    Journal: Proc Natl Acad Sci U S A; 2017 Sep 19; 114(38):10041-10046. PubMed ID: 28874582.
    Abstract:
    We investigated the structure of SiO2 glass up to 172 GPa using high-energy X-ray diffraction. 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 show that SiO2 first undergoes a change in Si-O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. 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. 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. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.
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