Continuous Sound Velocity Measurements along the Shock Hugoniot Curve of Quartz

Abstract

We report continuous measurements of the sound velocity along the principal Hugoniot curve of α quartz between 0.25 and 1.45 TPa, as determined from lateral release waves intersecting the shock front as a function of time in decaying-shock experiments. The measured sound velocities are lower than predicted by prior models, based on the properties of stishovite at densities below ∼7 g/cm^{3}, but agree with density functional theory molecular dynamics calculations and an empirical wide-regime equation of state presented here. The Grüneisen parameter calculated from the sound velocity decreases from γ∼1.3 at 0.25 TPa to 0.66 at 1.45 TPa. In combination with evidence for increased (configurational) specific heat and decreased bulk modulus, the values of γ suggest a high thermal expansion coefficient at ∼0.25-0.65 TPa, where SiO_{2} is thought to be a bonded liquid. From our measurements, dissociation of the molecular bonds persists to ∼0.65-1.0 TPa, consistent with estimates by other methods. At higher densities, the sound velocity is close to predictions from previous models, and the Grüneisen parameter approaches the ideal gas value.

Sound Velocity Measurement of Shock-Compressed Quartz at Extreme Conditions

“…At lower pressure of 200 GPa to 500 GPa, the sound velocity agrees with decay-laser shock results and DFT-MD results in Ref. [35]. But as the pressure goes above 600 GPa, our sound velocity data indicate a gentle increase in slope at high pressures from the whole data, compared with the previous theoretical and experimental results.…”

“…Most of results at higher pressure fall into the region bounded byV∆P/∆E average values (light blue line) and DFT-MD results (blue line) in Ref. [35]. The Grüneisen parameter decreases with shock temperature and pressure over the experimental range in general view.…”

“…[42]. In this figure, theoretical model results from the analytic solutions (KD model) from the release isentrope [27], density functional theory molecular dynamics (DFT-MD) calculations and empirical model (EM model) from wide regime equation of state (WEOS) [35] were also presented. Most of our measured sound velocities with errors are located in the region where theoretical model data results cover the whole pressure regions from 200 GPa to 1000 GPa, but slightly lower than those data from KD model, SESAME EOS table 7381 and 7386 for silica [42].…”

“…It is about 2 • − 3 • , depending on the VISAR system f value (focus distance-diameter) of lenses. Thus, a method for detecting the speed of sound by lateral unloading wave was proposed by Li et al in transparent materals [35] . The temporal lateral release trace in X-Y space and shock velocity u s are measured simultaneously by VISAR.…”

Ultra-High Pressure Dynamic Compression of Geological Materials

“…Hugoniot equation-of-state measurements have also be reported for fused silica samples to 1.6 TPa (McCoy et al, 2016b). Additional thermodynamic constraints can be obtained from measurements of bulk sound velocities that have been recorded for fused silica and quartz samples compressed into the liquid state to as high as 1.1 TPa in fused silica (McCoy et al, 2016a) and 1.45 TPa in quartz (Li et al, 2018). Both studies find that the Grüneisen parameter decreases with compression reaching a value of 0.66 at TPa pressure.…”