Microsecond-timescale dynamic compression of water probed by time-resolved X-ray Diffraction and Spectroscopy

The study of non-equilibrium transition dynamics for structural transformations in the s-to-μs regime is an emerging field in high pressure research. It is made possible by the development of a new device, the dynamic diamond anvil cell (dDAC). Such timescale lies between the characteristic time of shock compression (~nanoseconds) and of static compression (~seconds). Discrepancies between these two types of compression have been observed and experiments at an intermediate timescale of μs-ms are now helpful to resolve these disparities.

H₂O has been extensively studied both under static compression in the DAC and under laser-shock compression, allowing the observation of a large number of polymorphs [1, 2]. It has been one of the first system to be studied in the dDAC because of the implication for fundamental physics of diffusion-mediated properties and for the thermodynamic modeling of collision/impact events on ice-rich planetary bodies. Based on visual and Raman observation, super-compressed liquid water was first reported to crystallize into ice VII in the stability field of ice VI [3]. However, it was then reported that the metastable ice VII in the stability field of ice VI forms a high-density amorphous ice [4]. The determination of the nucleation and growth mechanisms were however unknown.

This work focuses on the use of a piezo-electrically driven dDAC to achieve a rapid pressure change on liquid water. Homogenous nucleation of ice is monitored using both time-resolved XRD at the ESRF ID09 beamline and spectroscopy. Our results reveal that at sufficiently high compression rate,water can be over-pressurized into the stability domain above the ice VII metastable melting line where the freezing into ice VII becomes more favourable as observed for the first time by XRD. Using a classical nucleation theory, we show that the nucleation time of ice VII can be directly linked to the overcompression. The deduced nucleation law unifies the results from the dDAC, the Z-machine ramp compression [5] and the laser ramp compression in the case of homogenous nucleation [6].

[1] J.A. Queyroux et al. PRL 125, 195501 (2020)

[2] M. Millot et al. Nature 569, 251 (2019)

[3] G.W. Lee et al. PRB 74, 134112 (2006).

[4] J-Y Chen et al. PNAS 108, 7685 (2011).

[5] Dolan D.Het al. Nat. Phys. 3, 339 (2007)

[6] Marshall M.C. et al. PRL 127, 135701 (2021)