High pressure elastic and plastic deformations of silica: In situ diamond anvil cell Raman experiments

Polyamorphism: Path to new high density glasses at ambient conditions

“…The sample reverts to 75% of Si IV with the decompression at ambient pressure. Recent molecular dynamic simulations [9,10] at 1000 K agree with Grimsditch [4] and Champagnon [18] experiments at room temperature for compression-decompression mechanism up to 20 GPa: the simulated density evolution with pressure compares well with the evolution of the intertetrahedral angle responsible for shift of the main band in Raman experiments [18]. The same agreement is observed between Huang et al simulations [10] and sound velocities determined from Brillouin experiments [4].…”

“…Grimsditch [4] observed an open hysteresis curve for sound velocity as function of pressure. Further XAS [14], neutron [15,16] and Raman [17,18] experiments confirm this observation. The exact structure of HDA silica is not clearly demonstrated up to now: even if a transition from 4 to 6 coordinated silicon is involved in the HDA phase, is the six-fold coordination preserved at ambient conditions?…”

“…1 compares the shifts of the main Raman bands with the density as determined by molecular dynamics simulations for silica as function of pressure. Our previous results on silica show that the LDA amorphous phase follows an elastic behavior up to a 8.6 GPa hydrostatic compression at room temperature [18]. This is attested by Raman spectra where all the lines coincide after and before compression.…”

“…In a recent paper [23] the anomalous density minimum of SiO 2 as function of temperature was interpreted as the region of the transition between the LDA and HDA amorphous phases. However relative density changes with fictive temperature are of the order of 1.5 · 10 À3 for a variation of T F of 250°C in SiO 2 [23] although density changes up to 20% are achieved in high pressure experiments [18]. Pressure parameter, alone or combined with temperature, appears then as the best way to generate a high density amorphous phase.…”

Molecular dynamics study of liquid silica under high pressure

“…It was demonstrated that α-cristobalite transforms into hp-cristobalite and finally into six-fold coordinated Stishovite, explaining that such two-stage densification is a ubiquitous mechanism [29]. The present author also showed that proportion of six-fold coordinated Si atoms starts increasing over 20 GPa monotonically; however, such coordination is not quenchable [22].…”