Crystal structure and thermal expansion of the δ-phase of O2-Ar solid solutions

X-ray investigations of the structure and thermal expansion of the metastable delta-phase of O2-Ar solutions are described. It is shown that the crystal structure δ-O2 is a direct analog of the cubic structure γ-O2. Supercooling of the solid γ-solutions of O2-Ar reduces their symmetry from Pm 3n with Z = 8(γ-O2) to I43d with Z = 64(δ-O2) due to the orientational ordering of the solid solutions of oxygen molecules. For δ-O2, the coefficients of thermal expansion are found to depend strongly on temperature and concentration of the solution.