Structural transformations including melting and recrystallization during shock compression and release of germanium up to 45 GPa

Abstract

Solid-solid and solid-liquid transformations were examined in Ge(100), using in situ xray diffraction measurements during uniaxial strain compression and release. For final stresses above 15.7 GPa, the Ge transformed to a highly textured tetragonal β-Sn phase. At 31.5 GPa and above, Ge transformed to the molten phase. Full stress release (uniaxial strain) from the β-Sn phase, from the melt boundary, and from the completely molten phase, resulted in reversion to an untextured cubic diamond (cd) phase. These findings demonstrate that the cd to β-Sn phase change is reversible, and that recrystallization from the liquid phase occurs on nanosecond timescales during release.

Real-time (nanoseconds) determination of liquid phase growth during shock-induced melting

“…We note that the previous observation of complete melting of shocked Ge at ~35 GPa in plate impact experiments ( 32) is consistent with the results in Fig. 4, since the earlier XRD measurements (32) were made at longer times (>150 ns) behind the shock front than the times shown in Fig. 4.…”

“…[100] Ge single crystals were chosen to examine the temporal growth of the liquid phase, for this first study, because of the following factors: high-pressure and high-temperature Ge data under static compression (28)(29)(30); continuum measurements on shockcompressed Ge single crystals (31); and recent XRD measurements on thin [100] Ge crystals in plate impact shock experiments (32). The plate impact XRD measurements, obtained more than 150 ns behind the shock front, demonstrated a fully liquid state at and above 35 GPa.…”

Structural Transformation and Melting in Gold Shock Compressed to 355 GPa

“…Although the fcc-bcc structural phase transition is counter intuitive, the melting transition observed at higher stresses -due to the concomitant temperature increase under shock compression -is consistent with previous similar observations of melting in shocked Si and Ge using in situ XRD [5,40,41] . Observed co-existence of the bcc phase and the molten state implies that the onset of melting in shocked Au is ~ 220 GPa.…”

The fast multi-frame X-ray diffraction detector at the Dynamic Compression Sector

“…In the following two frames, the peaks shift to lower angle as the release wave from the back of the sapphire reaches the Cu. Since detailed analysis of an impact experiment is complex and beyond this article's scope, for examples of analyses of similar XRD patterns, we refer the interested reader to articles analyzing similar patterns from this detector (Williams et al, 2020;Renganathan et al, 2019;Newman et al, 2018;Turneaure et al, 2018;Tracy et al, 2018). This example provides a good demonstation of the utility of multiframe collection, even in short-duration experiments.…”

“…To date, this system has been used successfully in impact experiments (Turneaure et al, 2016(Turneaure et al, , 2017Newman et al, 2018;Tracy et al, 2018;Renganathan et al, 2019), timeresolved small-angle X-ray scattering (SAXS) experiments on detonating explosives (Bagge-Hansen et al, 2015), and Kolsky bar experiments (Lambert et al, 2020). In these experiments, the detector system has demonstrated sufficient sensitivity to measure XRD powder rings and SAXS patterns from a single X-ray pulse.…”