Abstract
The recent discovery of a low-temperature endotherm upon heating hydrochloric-acid-doped ice VI has sparked a vivid controversy. The two competing explanations aiming to explain its origin range from a new distinct crystalline phase of ice to deep-glassy states of the well-known ice VI. Problems with the slow kinetics of deuterated phases have been raised, which we circumvent here entirely by simultaneously measuring the inelastic neutron spectra and neutron diffraction data of H2O samples. These measurements support the deep-glassy ice VI scenario and rule out alternative explanations. Additionally, we show that the crystallographic model of D2O ice XV, the ordered counterpart of ice VI, also applies to the corresponding H2O phase. The discovery of deep-glassy ice VI now provides a fascinating new example of ultrastable glasses that are encountered across a wide range of other materials.
Highlights
Problems with the slow kinetics of deuterated phases have been raised, which we circumvent here entirely by simultaneously measuring the inelastic neutron spectra and neutron diffraction data of H2O samples
A consequence of this is that pressure-quenched samples display an exothermic transient-ordering feature to ice XV upon heating at ambient pressure followed by the disordering phase transition to ice VI.[20,21]
Cooling hydrochloric acid (HCl)-doped ice VI/XV at pressures greater than ∼1.4 GPa leads to the appearance of a low-temperature endothermic feature before the onset of the transient ordering (cf. scan (3) in Figure 1a).[22−24] This endotherm has been assigned to the phase transition from a new hydrogen-ordered
Summary
We circumvent the potential complications associated with the D2O phases entirely, and carry out a combined inelastic neutron spectroscopy and neutron diffraction study of H2O samples. It is clear that the “standard” and deep-glassy ice VI are very similar from both the spectroscopic as well as the diffraction point of view, and both are very different from the hydrogen-ordered ice XV These observations rule out the ice β-XV scenario[23] and firmly link the low-temperature endotherm with deep-glassy states of ice VI.
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