Using coherent X-rays to follow dynamics in amorphous ices

Abstract

Amorphous ice plays an important role in our overall understanding of water's phase diagram.

Intrinsic Dynamics of Amorphous Ice Revealed by a Heterodyne Signal in X-ray Photon Correlation Spectroscopy Experiments

“…Our previous data from eHDA-grid samples show that eHDA enters a hyperdiffusive regime around T cryostat = 110 K, determined by a diffusion coefficient of D 0 = 3.1 Å 2 /s, a compressed exponential behavior (γ > 1.5), and a slight offset in the Q 2 dependence of the relaxation time, which could be related to stress relaxation inside the glassy matrix. Here we investigated temperatures above 110 K, showing the additional oscillatory behavior of g 2 .…”

“…Panels b and e of Figure summarize the characteristic times obtained from the fitting of the second exponential component (black dashed curve in panels a and d of Figure ) at different Q values at 115 and 117.5 K, respectively. An almost Q 2 dependence of the extracted relaxation rates is observed with an additional small offset . The green solid line depicts the result of a fit 1/τ = D 0 Q 2 + c with a diffusion coefficients ( D 0 ) of 12 and 63 Å 2 /s for 115 and 117.5 K, respectively, and an offset c of 0.0004 s –1 for both temperatures.…”

“…These spots appear as sharp Bragg peaks from crystalline ice in our WAXS curves (Figure b). We attribute them to the presence of a small amount of hexagonal ice that condensed on the sample during sample transfer . As the amount of these hexagonal ices is expected to be small and not embedded in the high-pressure ice matrix, it is reasonable to neglect its effect on the dynamics.…”

“…The bimodal scattering intensity in the WAXS pattern implies phase coexistence of eHDA and LDA and is consistent with our previous results. 4 , 30 , 34 The complete transition to LDA happens above 120 K ( T sample ≈ 125 K). This is slightly lower than the values from other studies of eHDA 30 , 35 but can be explained by a different sample preparation (see also the Supporting Information ).…”

Infrared Spectroscopy on Equilibrated High-Density Amorphous Ice

“…X-ray measurements confirm that eHDA is formed inside the grid-holes; the measured structure factor S ( Q ) is identical to the one measured from bulk samples. From X-ray studies on bulk and grid samples, − it is well-known that HDA upon warming transforms to the low-density state; the development of S ( Q ) is identical for both sample types. The process is exothermic and involves a volume change of 20%; for the grid samples, the expansion can take place perpendicular to the grid, as no windows restrain the motion.…”