Unusual morphology of equimolar Ar–Kr alloys

The transmission high electron energy diffraction (THEED) technique was employed for studying the structure of the equimolar Ar–Kr alloy, in which the thermodynamics predicts the maximum feasibility of phase separation. Deposition of preliminarily cooled gas mixtures was performed onto substrates cooled to 6 or 20 K. All diffraction patterns contained several sets of reflections against an appreciable background. Analysis of the data obtained during a warm-up from 6 to 33 K (at which the major part of argon was removed due to sublimation) as well as of the diffraction pattern from the “sandwich” (two successively deposited film of pure Ar and Kr) provided reliable arguments for the following conclusions. Actually, we have documented for the first time a phase separation of an Ar–Kr mixture, manifestations of which turned out to be oddly asymmetric as far as the behavior of the components involved is concerned. Upon deposition both onto 6 or 20 K the emerging sample contained two crystal phases of virtually pure argon with a small admixture of krypton. One of the Ar phases (fcc) did not cause a surprise, whereas the other was hcp with the a/c ratio close to the ideal value. The krypton component separated as a fine-grained glass-like state, possibly, with a low admixture of argon

Cluster approach to formation of nitrogen–rare gas cryoalloys

Structure of solid binary N₂–Kr and N₂–Ar solutions were studied by transmission electron diffraction (THEED). The samples were prepared in situ by deposition of gaseous mixture onto an Al substrate cooled to 20 K. The lattice parameters for low concentrations of one of the components were measured. The relative change of the lattice parameter per unit concentration is determined for N₂ impurity in Kr and Ar as well as for Kr and Ar in N₂. Analysis of the concentration dependence of the lattice parameters for low fractions of both components was performed within a cluster model in the three-particle approximation