Abstract
Recent Raman studies on the pressure-induced amorphization of ice in aqueous MX solutions (M = Li, K, Rb, Cs; X = Cl, Br, I) are reviewed. We have investigated the change of in situ Raman spectra as functions of pressure and temperature to establish the phase transition behavior of the ice in aqueous electrolyte solutions. It is found that the ice phase in LiCl·12H2O transforms first to an amorphous phase at ca. 0.5 GPa and then to a low temperature ice VII'-like phase at ca. 3 GPa. The transition pressures are much lowered by addition of LiCl salt, as compared with the corresponding results in pure ice phase (Ih → high density amorphous ice (HDA) → VII'). On the other hand, the ice in other aqueous MX solutions, such as MX = KCl, transforms to a crystalline phase of ice VII' (the frozen-in disorder of ice VII) at ca. 0.8 GPa. Thus, the obtained results show differences depending on the salts dissolved in water; the salt to form a glassy state upon quick cooling at a normal pressure transforms to an amorphous phase on compression, and the salt solution to form a crystalline state on cooling transforms to a crystalline ice phase, such as ice VII'.
