期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：27
页码：8216-8220
DOI：10.1073/pnas.1502438112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceIce-VII and ice-X phases are the most stable forms of ice at high temperature and extreme pressures, typical of the interiors of satellites and planets. The phase transition between them is a prototypical case of quantum-driven phenomenon, as it can be described as a quantum delocalization of protons in the middle of O-O distances. In this study, we investigate the effect of ions on such quantum effects. We show that the presence of ions significantly modifies the fundamental H-bond properties of water ices. This finding could challenge our present description of the physics of ice bodies, essentially based on the assumption of the properties of pure ice under high pressure. The richness of the phase diagram of water reduces drastically at very high pressures where only two molecular phases, proton-disordered ice VII and proton-ordered ice VIII, are known. Both phases transform to the centered hydrogen bond atomic phase ice X above about 60 GPa, i.e., at pressures experienced in the interior of large ice bodies in the universe, such as Saturn and Neptune, where nonmolecular ice is thought to be the most abundant phase of water. In this work, we investigate, by Raman spectroscopy up to megabar pressures and ab initio simulations, how the transformation of ice VII in ice X is affected by the presence of salt inclusions in the ice lattice. Considerable amounts of salt can be included in ice VII structure under pressure via rock-ice interaction at depth and processes occurring during planetary accretion. Our study reveals that the presence of salt hinders proton order and hydrogen bond symmetrization, and pushes ice VII to ice X transformation to higher and higher pressures as the concentration of salt is increased.
