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 $\text{Xe}{\left({\text{O}}_2\right)}_2$ 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.

• Received 17 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.014112