XRD Investigation of Novel Argon Filled-Ices to Extreme Pressures and Temperatures

Gas-filled ices are crystalline compounds of paramount importance to planetary science and potential energy storage applications, but the general understanding of their nature is challenged by a glaring inconsistency. Hydrogen and methane filled ices have been shown to be stable up to pressures of at least 90 GPa and 150 GPa, respectively, while homologous noble gas filled-ices were so far found to decompose just above a few GPa. On the othe hand, our recent Raman spectroscopy measurements show that argon filled-ice, when compressed fast enough through a narrow instability range: 5-10 GPa, remains well stable up to at least 40 GPa and also exhibits a phase transition from the previously known filled-ice phase ArH-IV to a new and unknown filled-ice phase. Here we propose to investigate this phase transition, the new structure and the related compression curves using powder XRD, to pressures of 50-80 GPa. This study will likely reconcile the inconsistency between filled ices.