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It has been known for decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below ≈160 K. This fact has recently been exploited to produce a « salty » high-pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallisation of aqueous solutions of LiCl∙RH2O and LiBr∙RH2O with R = 5.6 leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal-to-amorphous transition on decompression. This highly unusual behaviour constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degrees of freedom remaining completely random.

International audience; The richness of the phase diagram of water reduces drastically atvery high pressures where only two molecular phases, protondisorderedice VII and proton-ordered ice VIII, are known. Bothphases transform to the centered hydrogen bond atomic phase iceX above about 60 GPa, i.e., at pressures experienced in the interiorof large ice bodies in the universe, such as Saturn and Neptune,where nonmolecular ice is thought to be the most abundant phaseof water. In this work, we investigate, by Raman spectroscopy upto megabar pressures and ab initio simulations, how the transformationof ice VII in ice X is affected by the presence of saltinclusions in the ice lattice. Considerable amounts of salt can beincluded in ice VII structure under pressure via rock–ice interactionat depth and processes occurring during planetary accretion. Ourstudy reveals that the presence of salt hinders proton order andhydrogen bond symmetrization, and pushes ice VII to ice X transformationto higher and higher pressures as the concentration ofsalt is increased.