Unraveling He-H2O compounds stability and thermodynamics at extreme pressure and temperature conditions

The aim of this proposal is to investigate the stability, structures, phase boundary lines and thermomechanical properties of intriguing He-H2O compounds at extreme P and T (P = 0–120 GPa, T = 300–2500 K) predicted by first-principle calculations. The observation of such compounds could drastically impact the current models of giant icy planets. We plan to load He-H2-O2 ternary mixtures in the DAC and induce the formation of H2O in He at a given pressure. Doing so will provide a controlled way to reveal stable He-bearing-ice compounds. These compounds are expected to exhibit exotic behaviours such as a highly diffusive, ‘superionic’ character at high T involving both helium atoms and protons. In previous runs (HC-2185, HC-3952, HC-4677), we have investigated the properties and stability fields of superionic phases in pure H2O ice by XRD on laser-heated samples in the diamond anvil cell (DAC). A similar approach will be operated here.