X-ray diffraction of ramp-compressed aluminum to 475 GPa

Abstract

We report on a series of experiments that use high-power lasers to ramp-compress aluminum (Al) up to 475 GPa. Under this quasi-isentropic compression, Al remains in the solid state and two solid–solid phase transformations are observed. In situ x-ray diffraction is performed to detect the crystal structure. A velocimetry diagnostic measures particle velocities in order to infer the pressure in the Al sample. We show that a solid–solid phase transition, consistent with a transformation to a hexagonal close-packed (hcp) structure, occurs at 216 ± 9 GPa. At higher pressures, a transformation to a structure consistent with the body-centered cubic (bcc) structure occurs at 321 ± 12 GPa. These phase transitions are also observed in 6061-O (annealed) Al alloy at 175 ± 9 GPa and 333 ± 11 GPa, respectively. Correlations in the high-pressure crystallographic texture suggests the close-packed face-centered cubic (fcc) (111), hcp (002), and bcc (110) planes remain parallel through the solid–solid fcc–hcp and hcp–bcc transformations.

Ultra-High Pressure Dynamic Compression of Geological Materials

“…This may reflect over-pressurization of the equilibrium phase boundary under the short timescales of dynamic compression. In the case of aluminum, however, phase transitions from a face-centered-cubic structure to hexagonalclose packed (hcp) and body-centered-cubic (bcc) phases at ∼200-300 GPa under laser-based ramp loading are in good agreement with transition pressures from static compression data and theoretical calculations (Akahama et al, 2006;Fiquet et al, 2018;Polsin et al, 2018). Understanding possible kinetics factors associated with phase transformations under ultrahigh pressure-temperature conditions is an important goal for future experiments.…”

“…Due to the limitations of available X-ray sources, such studies were primarily restricted to examination of single crystals at relatively low pressure. The application of brighter X-rays sources including laser-plasma sources (i.e., X-ray emission by highly ionized atoms produced by laser-matter interactions) (Wark et al, 1987(Wark et al, , 1989, synchrotrons (Gupta et al, 2012), and free-electron lasers (Milathianaki et al, 2013) to dynamically compressed materials has now made it possible to extend such studies to terapascal pressures (Wang et al, 2016;Polsin et al, 2018;Wicks et al, 2018).…”

“…Although laser-plasma sources are very bright, the source is uncollimated and only a small fraction of the generated X-rays pass through the sample. To date, this technique has mostly been applied to high-symmetry and/or high-atomicnumber samples such as MgO, Fe-Si alloys, or other materials that produce a few intense diffraction lines (Coppari et al, 2013;Wang et al, 2016;Polsin et al, 2018;Wicks et al, 2018).…”

Molecular dynamics simulations of inelastic x-ray scattering from shocked copper

“…Shock compression is highly entropic, and as a result for most metals the Hugoniot (the locus of points that can be reached by shock compression) crosses the melt curve at pressures of order 100 -300 GPa [66][67][68] . However, with controlled laser pulses, shaped in time, or by compressing materials via multiple shocks (which can in principle be induced by appropriate target design 69 ), the application of high pressure can be achieved in a ramped manner 57,[70][71][72][73][74] , without the compression wave steepening into a shock. This so-called 'quasi-isentropic' (QI) compression has been shown to keep material solid well into the TPa regime [75][76][77][78][79][80] .…”

Investigating off-Hugoniot states using multi-layer ring-up targets

“…A quasi-monochromatic X-ray backlighter from a laser-plasma source could then be used to record X-ray diffraction measurements at peak compression. This method has been used at the Omega laser facility 31 to ramp compress Al to 475 GPa 32 and Mo, Sn and Fe–Si alloys to above 1 TPa 33 – 35 . While there has been significant success using this approach, the advent of X-ray Free Electron Lasers (XFELs) and in particular high energy density beamlines that pair these intense X-ray sources with nanosecond lasers 36 – 38 , has sparked significant interest in performing ramp compression experiments using these facilities 39 .…”