Vie de l'Institut - Institut de minéralogie et de physique des milieux condensés

 Salty ice under pressure

A. Marco SAITTA (IMPMC)

IMPMC, Université P. et M. Curie, 4, Place Jussieu, 75005 Paris  
Salle de Conférence - 401
4ème étage
Tour 23
Couloir 22-23

Résumé:
Water contains significant amounts of dissolved ionic species. Nonetheless, surprisingly little experimental attention has been paid on the high pressure behaviour of “salt water” compared to pure water. In a recent study combining neutron diffraction and molecular dynamics simulations we showed the existence of a reversible polyamorphic transition in LiCl:6D2O between a high-density (HDA) and a very-high-density amorphous (VHDA) form, taking place abruptly at 120 K and 2 GPa under annealing at high pressure. We suggest that the transition is linked to a local structural reorganization of water molecules around the Li ions.

Under further annealing at high pressure (~4GPa), the salty-VHDA amorphous crystallizes in a new and unexpectedly simple salt hydrate which can be regarded as an ‘alloyed’ high-pressure ice phase. Such ‘salty’ ice VII has significantly different structural properties compared to pure ice VII. Our study strongly suggests that there is a whole new class of salt hydrates based on various kinds of solutes and high pressure ice forms. If these exist in nature in significant quantity, their physical properties would be highly relevant for the understanding of icy bodies in the solar system.

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