Structure of the Delta Phase in the Argon–Oxygen System

The crystal structure of the δ phase of the argon–oxygen system has been investigated using powder techniques. This phase, which exists in the composition range of 60%–90% O2, has a body-centered cubic unit cell with a0 = 13.23 Å. The a0 for the phase closely approximates 2a0 for γ-O2, and the diffraction patterns have marked similarities. The structure was found to be a superlattice or a close analog of the γ-O2 structure with definite segregation of the Ar and O2 within the unit cell. Although the exact nature of this segregation was not determined, the basic type is presented and three possible modifications of this type that meet specific requirements are discussed. The composition limits for the phase are understandable in terms of the occupancy of the sites in the proposed structure.

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