Oxygen/noble gas binary phase diagrams at 296 K and high pressures

Abstract

The binary phase diagrams of ${\text{O}}_{2}/\text{rare}$ gas (He, Ne, Ar, and Xe) mixtures have been measured at 296 K up to 20 GPa in a diamond-anvil cell. The boundary lines were determined by visual observation and by the Raman frequency of the ${\text{O}}_{2}$ vibron mode. The ${\text{O}}_{2}\text{-He}$ phase diagram is of eutectic type with a liquid-liquid miscibility gap and complete immiscibility in the solid phase. The ${\text{O}}_{2}\text{-Ne}$ phase diagram is of eutectic type with partial immiscibility in the solid phase. The ${\text{O}}_{2}\text{-Ar}$ phase diagram is of azeotrope type and three different structures of $\text{Ar}/{\text{O}}_{2}$ solid solutions have been identified. The ${\text{O}}_{2}\text{-Xe}$ phase diagram is of peritectic with eutectic type. The stoichiometric compound $\text{Xe}{({\text{O}}_{2})}_{2}$ is observed and characterized as a laves phase with a cubic structure isomorphous to ${\text{MgCu}}_{2}$. A qualitative understanding of these various diagrams is reached by the comparison of the effective hard-sphere diameters of the various species in the 10 GPa range. Some of the usefulness of the knowledge of these binary phase diagrams is highlighted: as a reference data set to test theoretical calculations on mixtures; to grow single crystal of ${\text{O}}_{2}$ in a rare-gas pressure medium; and to synthesize rare-gas oxides at high pressure.