Experiments indicating a second hydrogen ordered phase of ice VI

Abstract

We report on the discovery and characterization of ice β-XV, which represents the second hydrogen ordered polymorph related to ice VI.

Deep-Glassy Ice VI Revealed with a Combination of Neutron Spectroscopy and Diffraction

“…21 A major misunderstanding in ref. 22 is also that the ice XV to ice VI phase transition does not begin at 129 K but just above 100 K as shown in Figure 1(a) and elsewhere. [19][20] In contrast to the β-ice XV scenario, we argued that the low-temperature endotherm arises from the glass transition of deep-glassy ice VI which becomes increasingly more relaxed or 'deeper' as the cooling pressure is increased.…”

“…The ND data of H2O ice XV presented here provides the first evidence for this assumption. Furthermore, we note that the proposed β-ice XV, which has been suggested to have a different space group symmetry compared to ice XV, 22 would have to display a significantly different ND pattern compared to the one of deep-glassy ice VI and that of ice XV.…”

“…This confirms that the new lowtemperature endotherm is indeed associated with the glass transition of deep-glassy ice VI, which is structurally very close to 'standard' ice VI. An INS spectrum of β-ice XV, which has been suggested to be more and differently ordered than ice XV, 22 would have to display a spectrum markedly different from both ice VI and ice XV. 7 ordering can be seen from the appearance of the ~448 cm -1 ice XV feature above 100 K and its subsequent disappearance at 138 K. Slow-cooling back to 80 K leads to significant increases in intensity of this feature illustrating, in line with earlier studies, 19-20 that slow-cooling produces a much more ordered ice XV compared to the states accessible during the transient ordering upon heating which is also consistent with the schematic shown in Figure 1(b).…”

“…22,27 Changes in the relative intensities of modes in micro-Raman spectroscopy can arise from preferred orientation effects 35 which clearly play a role as can be seen from the comparison of nominally identical ice VI/XV materials in the literature. 7,22,27,29,[36][37][38] However, the shift in the coupled O-H stretching mode region may be a sensitive indicator for the strain levels in deep-glassy ice VI. In fact, Raman spectroscopy has been demonstrated to be a very powerful technique for detecting strain in a wide range of different materials.…”

Deeply supercooled aqueous LiCl solution studied by frequency-resolved shear rheology

“…The pure (undoped) ice VI sample was prepared as described in Ref. 62. In brief, 600 µl of pure water were frozen to hexagonal ice at 77 K, compressed to 1.0 GPa, and heated to 250 K (at 20-25 K/min).…”