Structure and disorder in ice VII on the approach to hydrogen-bond symmetrization

Malcolm Guthrie, R. Boehler, J. J. Molaison, B Haberl, A. M. dos Santos, C Tulk

Research output: Contribution to journalArticlepeer-review


We have collected neutron-diffraction data of sufficient quality for structural refinement from deuterated ice VII to over 60 GPa. At these pressures, we are approaching the onset of molecular dissociation where the water molecule should be significantly distorted. We fitted our data with both the conventional structural model for ice VII and a recently proposed “interstitial” model. We found these to be statistically indistinguishable and, therefore, adopted the conventional model in this work. Our refinements yield the first direct experimental determination of the molecular structure in this pressure regime. They show a clear elongation of the covalent bond, the rate of which rapidly increases with pressure, indicating we have entered a distinct regime on the
approach to ice X. In addition, we have directly measured the pressure dependence of the separation of the two equivalent deuteron sites along the hydrogen bonds, which provides an upper bound on the hydrogen-bond
centering pressure.
Original languageEnglish
JournalPhysical review B: Condensed matter and materials physics
Publication statusPublished - 23 May 2019

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