COMPUTER-SIMULATION STUDIES OF ORDERED STRUCTURES FORMED BY RARE-GASES SORBED IN ZEOLITE-RHO

Computer simulations of the energies and structures of krypton and argon in zeolite rho at high sorbate loadings are reported here. The results, taken together with previous simulations of xenon, show that all these gas atoms sorbed in the zeolite cages of diameter approximately 11 angstrom exhibit ordered structures at high loadings. The ordering does not appear to be greatly affected by increases in temperature and thus is most likely due to packing considerations. Several types of order were observed, depending upon the size of the sorbate atom and the cage loading. Basically, all were of cubic symmetry, reflecting the symmetry of the cages. Omitting the central sorbate atom that was usually present, the structures can be described as simple cube (8 Xe atoms), distorted face-centered-cubic (14 Ar or Kr atoms), and a more complex but still cubic structure (20 Ar atoms). It is noted that cages of this size are found in many zeolite crystals.