Abrupt crystallization from shock-compressed CaSiO3 glass

Abstract

We have performed in situ time-resolved X-ray diffraction at ~100 GPa on laser-shocked CaSiO3 glass to investigate the glass-to-crystal transition. At this extreme pressure, we observe the ultrafast crystallization of the CaSiO3 perovskite structure from the compressed amorphous phase, with a typical nucleation time of 1.69 +/- 0.10 ns and a final grainsize of ~20 nm. The grain size temporal evolution suggest a diffusion controlled transformation. Moreover, the observed concomitant explosive grain growth together with the release wave arrival into shocked CaSiO3 also suggests a role of the release in the nucleation process.

Figures (4)

• Figure 1: (a) Schematic of the experimental configuration and target design. (b) 2D X-ray diffraction (XRD) patterns signal acquired with the flatpanel detector, showing on left the amorphous signals from the unshocked sample, and on right crystallized Pv-CaSiO$_3$ signals from the shot sample, corresponding to a pump-probe delay of 8.4 ns.
• Figure 2: (a) Selection of azimuthally integrated diffraction pattern, obtain with a 11 keV incident x-ray energy, ordered as a function of the arrival time of the shock in CaSiO$_3$. The average pressure for those shots is $108\pm11$ GPa. The vertical dashed lines correspond to the position of the Pv-CaSiO$_3$ ambient peaks. (b) Patterns at 1.8 ns and 2.4 ns with the unshocked ambient signal subtracted, highlighting the presence of a compressed amorphous diffuse signal, characterized by 2 broad peaks around 27$^\circ$ and 35$^\circ$.
• Figure 3: (a) Grain size of Pv-CaSiO$_3$ extracted from the diffraction peaks with the Warren-Averbach method warren_effect_1950. Best fitting result of formula (\ref{['eq_gg']}) is given with $n=2$ in the coalescence/coarsening regime and plotted with a dotted black line. (b) Time evolution of the integrated Pv-CaSiO$_3$ peaks intensity. Those values are extracted for all CaSiO$_3$ samples with similar thickness; therefore, they reflect the evolution of the crystal proportion in the sample. (c) Time evolution of pressure at the interface of ablator and LiF obtained through MULTI hydrodynamic simulation (see Fig. S2 in supplementary), calibrated on VISAR results. Two different release wave breakouts are determined from it.
• Figure 4: (a) Estimation of nucleation rate dependence with temperature, calculated from Eq. (\ref{['nucleation']}) for CaSiO$_3$; the curve is calculated using a 7200 K melting temperature at 108 GPa for CaSiO$_3$ given by the melting curve of yin_davemaoite_2023. The qualitative representation of nucleation rate for heterogeneous nucleation is shown in blue dotted line. The calculated Hugoniot temperature condition of CaSiO$_3$ glass at 108 GPa is by the grey vertical region. (b) Phase diagram of CaSiO$_3$ with calculated Hugoniot of CaSiO$_3$ glass, and schematic of release path from CaSiO$_3$ glass compressed at 108 GPa. Melting region boundaries are determined from three different melting curves braithwaite_melting_2019hernandez_ab_2022yin_davemaoite_2023.