Structural Studies of Several Distinct Metastable Forms of Amorphous Ice

Abstract

Structural changes during annealing of high-density amorphous ice were studied with both neutron and x-ray diffraction. The first diffraction peak was followed from the high- to the low-density amorphous form. Changes were observed to occur through a series of intermediate forms that appear to be metastable at each anneal temperature. Five distinct amorphous forms were studied with neutron scattering, and many more forms may be possible. Radial distribution functions indicate that the structure evolves systematically between 4 and 8 angstroms. The phase transformations in low-temperature liquid water may be much more complex than currently understood.

Polyamorphism of Ice at Low Temperatures from Constant-Pressure Simulations

“…As observed by X-ray scattering in Ref. [9,10], with increasing annealing temperature the interstitial region around 3.5Å is depleted and the second shell peak around 4.4Å grows.…”

“…Recently several new experimental results [6,7,8,9,10,11] raised new questions about the polyamorphism of ice.…”

“…It has been called very high-density amorphous ice (VHDA) and characterized experimentally using neutron diffraction [8]. Moreover, experiments [9,10] show that by heating HDA to temperatures intermediate between 80 K and 110 K the sample can be trapped in an apparent continuum of metastable structures between HDA and LDA. This suggests that there might be no sharp transition between the two forms.…”

“…In fact, the density as well as the RDF of our RP decompressed from 4.5 kbar (not shown) is very similar to that of HDA' at p = 0. A relaxation of O then becomes possible upon progressive increase of the temperature [9,10,11]; the system approaches the global minimum of F HDA (V ) and at a certain point undergoes a transition to a more stable LDA form. As observed by X-ray scattering in Ref.…”

Two-Dimensional Infrared Spectroscopy of Isotope-Diluted Low Density Amorphous Ice

“…The structure of amorphous ice is a crucial aspect in a comprehensive understanding of the thermodynamic properties of water [7]; in particular in light of the liquid-to-liquid phase transition hypothesis put forward by Stanley and coworkers to account for the anomalous thermodynamic properties of water [8,9]. That is, two distinct liquid phases in the deeply supercooled regime are predicted (low-density liquid LDL and high-density liquid HDL), which are believed to be associated with the corresponding amorphous ice phases, LDA and HDA, respectively [10][11][12][13].…”