X-ray studies of the transformation from high- to low-density amorphous water

Abstract

Here we report about the structural evolution during the conversion from high-density amorphous ices at ambient pressure to the low-density state. Using high-energy X-ray diffraction, we have monitored the transformation by following in reciprocal space the structure factor S OO ( Q ) and derived in real space the pair distribution function g OO ( r ). Heating equilibrated high-density amorphous ice (eHDA) at a fast rate (4 K min –1 ), the transition to the low-density form occurs very rapidly, while domains of both high- and low-density coexist. On the other hand, the transition in the case of unannealed HDA (uHDA) and very-high-density amorphous ice is more complex and of continuous nature. The direct comparison of eHDA and uHDA indicates that the molecular structure of uHDA contains a larger amount of tetrahedral motives. The different crystallization behaviour of the derived low-density amorphous states is interpreted as emanating from increased tetrahedral coordination present in uHDA. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Long-Range Structures of Amorphous Solid Water

“…Therefore, we can conclude that the molecular structure of the vapor-deposited p-ASW sample deposited at 80 K exists within the same energy landscape megabasin of LDA. Our results are consistent with previous findings, 40 , 42 , 56 and additionally extend the previously explored coordination shells up to a distance of 23 Å.…”

“… (a) Full-range structure factor, S OO ( Q ), at 80 K for p-ASW deposited on Kapton at 80 K for 4 h. LDA-I and LDA-II (Mariedahl et al .) 42 are shown for comparison; both samples were measured under the same conditions. (b) S OO ( Q ) curves at a short Q-range.…”

“…Crystallization is observed at temperatures above T m = 130 K ( T s = 140 K) by the appearance of Bragg peaks at Q = 2.79 and 3.28 Å –1 , both of which are related to ice Ic and ice Ih. 42 Some Bragg peaks strictly related to ice Ih, e.g ., Q = 3.04 Å –1 , are observed at higher temperatures. Thus, we conclude that ASW transforms from LDA to the so-called stacking disordered ice I (ice I sd ) at around T s = 140 K. 60 − 66 A direct comparison of crystalline ice derived from p-ASW (warmed to T s = 160 K), LDA-I (warmed to T s = 150 K), and LDA-II (warmed to T s = 160 K) is shown in Figure S6 .…”

“… 46 A detailed description of the data analysis can be found in our previous publication; 40 the current data set was taken during the same beam time and analyzed in the same way. The LDA data 42 shown in Figure 2 a were collected under identical conditions.…”

The physics and chemistry of ice

“…Amann-Winkler et al [30] focus on transitions of ice in the absence of impurities reviewing connections between two distinct amorphous states of ice with different density (high-and low-density amorphous ice, HDA and LDA) to the occurrence of two distinct liquid phases with their specific density [31][32][33][34][35]. The glass transition in both amorphous states, LDA and HDA, was investigated using different experimental techniques and discussions on this have provoked controversy in recent years'.…”