Dynamic X-ray diffraction observation of shocked solid iron up to 170 GPa

Abstract

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.X-ray diffraction | iron phase diagram | shock-compressed iron | Earth core | dynamic compression

Quantum molecular dynamics of warm dense iron and a five-phase equation of state

“…The principle shock Hugoniot passes through those two phases before begining to melt at about 195 GPa and 4800 K, completion of melt is then at about 290 GPA and 5850 K. The gamma phase extends to a maximum pressure of 100 GPa. It has been speculated in the past that there exists a phase other than epsilon below the melt curve at higher pressures than this, but current theory [6] and experiment [58,59] do not support this and we have no such phase in our EOS. The epsilon phase has been shown through DFT studies to be the stable ground-state phase up to 7 TPa [60], where fcc, and at much higher pressure bct phases become the stable phase.…”

Shock Melting Curve of Iron: A Consensus on the Temperature at the Earth's Inner Core Boundary

“…We shocked iron up to the solid‐liquid mixed‐phase region to obtain the melting temperatures of iron according to the previous sound velocity measurements and phase diagram of iron under shock loading (Denoeud et al, 2016; Harmand et al, 2015; Nguyen & Holmes, 2004). The shock temperature ( T H ) of the mixed‐phase iron is on the melting curve ( T M ) at the Hugoniot pressure ( P H ).…”

Phase transition of iron-based single crystals under ramp compressions with extreme strain rates

“…Phase transition under high pressures has been attracting a great interest in condensed matter physics (Duvall and Graham, 1977;Kadau et al, 2002;Takahashi and Bassett, 1964), geophysics (Coppari et al, 2013;Shen et al, 2016), materials science (Li et al, 2014;Talonen and Hä nninen, 2007) and engineering mechanics (Guthikonda and Elliott, 2013). Recent breakthrough on the ultrafast X-ray diagnostics (Denoeud et al, 2016;Milathianaki et al, 2013) under dynamic loadings has prompted a renewed interest in phase transformation of iron from α (bcc) to ε (hcp) phase which is a prototype of martensite phase transition under high pressures. In the past thirty years, mechanical behaviors of materials exhibiting martensite phase transition have been simulated with methods at different hierarchical levels from macroscopic phenomenological models to microscopic-mechanism-based models.…”