Single-Crystal Elasticity of Salty-Ice at High Pressures

Abstract:

Water ice exists in various planetary bodies in the universe. Among its high-pressure phases, ice-VII and ice X are suggested to be present in moderate to large-size icy planetary bodies. Experimental studies on the phase transition from ice-VII to ice X and physical properties of these two phases are thus significant in understanding the structure and dynamic evolution of icy planets. At 300 K, ice VI transforms into ice-VII near 2 GPa. Ice-VII has been reported to further change into the dynamically disordered ice-VII at 40-58 GPa. At higher pressures, the dynamically disordered ice-VII will transform into ice X but the phase boundary is still under debate. More importantly, there are no experimental results on the single-crystal elasticity of ice X at high pressures because of the difficulty in synthesizing single-crystal ice samples. In addition, the influence of the transition from ice-VII to ice X on the density and elasticity remains poorly constrained. In this study, we have performed Brillouin measurements on the single-crystal elasticity of salty ice (0.5 mol/L NaCl) up to 94 GPa at 300 K in the high-pressure laboratory in the University of Science and Technology of China. We well constrained the change in elasticity across the transition from ice-VII to ice X and provide the first-experimental constraints on the single-crystal elasticity of ice X up to 94 GPa at 300 K. These results are important for understanding the composition and velocity structure of icy planets.