Abstract
Silica glass has been shown in numerous studies to possess significant capacity for permanent densification under pressure at different temperatures to form high density amorphous (HDA) silica. However, it is unknown to what extent the processes leading to irreversible densification of silica glass in cold-compression at room temperature and in hot-compression (e.g., near glass transition temperature) are common in nature. In this work, a hot-compression technique was used to quench silica glass from high temperature (1100 °C) and high pressure (up to 8 GPa) conditions, which leads to density increase of ~25% and Young’s modulus increase of ~71% relative to that of pristine silica glass at ambient conditions. Our experiments and molecular dynamics (MD) simulations provide solid evidences that the intermediate-range order of the hot-compressed HDA silica is distinct from that of the counterpart cold-compressed at room temperature. This explains the much higher thermal and mechanical stability of the former than the latter upon heating and compression as revealed in our in-situ Brillouin light scattering (BLS) experiments. Our studies demonstrate the limitation of the resulting density as a structural indicator of polyamorphism, and point out the importance of temperature during compression in order to fundamentally understand HDA silica.
Highlights
In this study, we compressed samples of silica glass to pressures up to 8 GPa, held them at 1100 °C (Tg ≈ 1200 °C) for 30 minutes, and rapidly quenched them to room temperature before releasing the pressure
Densification of silica glass as a function of quench pressure from the hot-compression in this study is shown in Fig. 1, together with data from the cold-compression at room temperature done by Rouxel et al.[15] and Deschamps et al.[12], at 400 °C by Mackenzie[13] and Arndt and Stöffler[17], at 700 °C by Poe et al.[18], at 900 °C by Hofler and Seifert[19]
The above observations show that temperature facilitates the densification of silica glass under pressure, probably by enabling different structural transformations otherwise not possible at room temperature
Summary
We compressed samples of silica glass to pressures up to 8 GPa, held them at 1100 °C (Tg ≈ 1200 °C) for 30 minutes, and rapidly quenched them to room temperature before releasing the pressure. The structure and properties of HDA silica obtained in the hot-compression were found to be distinct from those of the cold-compressed one in both experimental characterizations such as X-ray diffraction, Raman and BLS, and in MD simulations. In-situ BLS studies under high temperature and high pressure provide solid evidences that the thermal and mechanical stability of hot-compressed and cold-compressed HDA silica are very different. Our study shows the limitation of the resulting density as a structural indicator of polyamorphism and the importance of temperature during compression in order to fundamentally understand the polyamorphic transitions in silica glass
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