Sound velocity of iron up to 152 GPa by picosecond acoustics in diamond anvil cell

Abstract

High‐pressure method combining diamond anvil cell with picosecond ultrasonics technique is demonstrated to be a very suitable tool to measure the acoustic properties of iron up to 152 GPa. Such innovative approach allows to measure directly the longitudinal sound velocity under pressure of hundreds of GPa in laboratory, overcoming most of the drawbacks of traditional techniques. The very high accuracy, comparable to piezoacoustics technique, allows to observe the kink in elastic properties at the body‐centered cubic–hexagonal close packed transition and to show with a good confidence that the Birch's law still stands up to 1.5 Mbar and ambient temperature. The linear extrapolation of the measured sound velocities versus densities of hcp iron is out of the preliminary reference Earth model, arguing for alloying effects or anharmonic high‐temperature effects. A comparison between our measurements and shock wave experiments allowed us to quantify temperature corrections at constant pressure in ~−0.35 and ~−0.30 m s−1/K at 100 and 150 GPa, respectively. More in general, the here‐presented technique allows detailed elastic and viscoelastic studies under extreme thermodynamic conditions on a wide variety of systems as liquids, crystalline, or polycrystalline solids, metallic or not, with very broad applications in Earth and planetary science.

Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models

“…Only very recently, measurements of acoustic echoes in samples compressed in diamond anvil cells became possible thanks to the developments in time-resolved pump-probe techniques (laser ultrasonics), both in the nanosecond time scale (Chigarev et al, 2008) and in the picosecond time scale (Decremps et al, 2008). Measurements on iron provided V P and V S up to 23 GPa (Chigarev et al, 2008) and of the only V P up to 152 GPa (Decremps et al, 2014).…”

“…Accordingly, these measurements are more largely dependent on specific choice of ruby pressure scale and iron EOS. Results obtained by ISLS (Crowhurst et al, 2004) and by picosecond acoustics (Decremps et al, 2014) are reported in Figure 5. Densities have been determined starting with the reported pressures and using the EOS by Mao et al (1990), which is consistent with the old ruby scale, and then using our reference EOS to reassess the pressure values.…”

“…This, together with the fact Figure 5 Compressional sound velocity as a function of density as derived from pulsed-laser techniques. Violet crossed diamonds (Crowhurst et al, 2004); orange lined diamond (Chigarev et al, 2008); blue open diamonds (Decremps et al, 2014). Lines are linear fits to the experimental data sets.…”

“…Within a quasi-harmonic approximation, V P is expected to scale linearly with density, irrespective Figure 6 Compressional sound velocity as a function of density. Violet crossed diamonds (Crowhurst et al, 2004); blue open diamonds (Decremps et al, 2014); red open circles (Antonangeli et al, 2004b;; green lined circles (Ohtani et al, 2013). The star is the ultrasonic determination reported in (Mao et al, 1998).…”

“…Figure 8 Compressional sound velocity as a function of density. Black squares are selected data sets (same as Figures 6 and 7) obtained under static compression at 300 K (Mao et al, 1998;Crowhurst et al, 2004;Antonangeli et al, 2004b;Ohtani et al, 2013;Decremps et al, 2014). The solid line is a linear regression across the static data.…”