Effect of salt on the H-bond symmetrization in ice
Résumé
The richness of the phase diagram of water reduces drastically at
very high pressures where only two molecular phases, protondisordered
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.