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Abstract
The structure of hydrous amorphous SiO2 is fundamental in order to investigate the effects of water on the physicochemical properties of oxide glasses and magma. The hydrous SiO2 glass with 13 wt.% D2O was synthesized under high-pressure and high-temperature conditions and its structure was investigated by small angle X-ray scattering, X-ray diffraction, and neutron diffraction experiments at pressures of up to 10 GPa and room temperature. This hydrous glass is separated into two phases: a major phase rich in SiO2 and a minor phase rich in D2O molecules distributed as small domains with dimensions of less than 100 Å. Medium-range order of the hydrous glass shrinks compared to the anhydrous SiO2 glass by disruption of SiO4 linkage due to the formation of Si–OD deuterioxyl, while the response of its structure to pressure is almost the same as that of the anhydrous SiO2 glass. Most of D2O molecules are in the small domains and hardly penetrate into the void space in the ring consisting of SiO4 tetrahedra.
Highlights
IntroductionSiO2 glass is densified by compression with the change in medium-range order in the pressure region up to about 10 GPa [2,4,8]
Silica glass is the most fundamental, fully polymerized network glass whose structure and properties under pressure have long been of interest as an important analog material of silicate magma [1,2,3,4,5,6,7,8,9].For the structural aspect, SiO2 glass is densified by compression with the change in medium-range order in the pressure region up to about 10 GPa [2,4,8]
It is known that the silicate glass with high water content undergoes the glass-in-glass phase separation at a low temperature [11]
Summary
SiO2 glass is densified by compression with the change in medium-range order in the pressure region up to about 10 GPa [2,4,8]. SiO2 glass becomes fully densified glass by room temperature compression to the pressure of 9 to 13 GPa, of which the density is about 20% higher than ordinary SiO2 glass at ambient conditions [8]. It is known that the molecular water becomes the dominant water species in the silicate glasses with increasing total water content [10,11]. It is not yet well understood how the molecular water is incorporated into the silicate glasses
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