Ice VII from aqueous salt solutions; From a glass to a crystal with broken H-bonds

Klotz, S.*; Komatsu, Kazuki*; Pietrucci, F.*; Kagi, Hiroyuki*; Ludl, A.-A.*; Machida, Shinichi*; Hattori, Takanori   ; Sano, Asami   ; Bove, L. E.*

It has been known since 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 crystallization of aqueous solutions of LiCl5.6HO and LiBr5.6HO 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 behavior constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degree of freedoms remaining completely random.