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(Color online) Diffraction pattern of equimolar Ar-Kr sample. Deposition and registration temperatures are 6 K.
Source publication
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 20K. All diffraction patterns contain...
Contexts in source publication
Context 1
... of sub-LN equimolar Ar-Kr gas mixtures onto a 6 K substrate resulted in polycrystalline weakly textured layers as shown in Fig. 1. We failed to determine the structure and morphology of this sample within a monophase assumption. Besides the reflections with inter-plane distances 3.062, 2.656, 1.882, and 1.602 Å, which correspond to indices, respectively, (111), (200), (220), and (311) of a fcc Ar structure with a lattice parameter of 5.323 Å, the pattern ...
Context 2
... with inter-plane distances d 1 = 3.249 Å (S 1 = 1.934 Å -1 ) and d 2 = 2.854 Å (S 2 = 2.201 Å -1 ), which needed a special analysis. It should be noted here that reflex d 2 , because of its low intensity and large spread, was identified poorly so that its very existence caused doubt. In Fig. 2 we present a densitogram of the pattern plotted in Fig. 1. Subtraction of the noncoherent background revealed that, apart from reflections fcc Ar and d n , the pattern includes a rather intensive halo at small diffraction angles around S = 2.16 Å ...
Citations
The structure characteristics of Ar−Kr mixtures deposited under special conditions have been investigated in the whole interval of concentrations applying the transmission electron diffraction technique (THEED). The samples were prepared in situ by condensing a gas mixture preliminary cooled down to the sub-liquid-nitrogen level onto substrates at T = 6 K and 20 K. The experimental results show that the structure and morphology of the Ar−Kr condensates are dependent on the nucleation dynamics prevailing in the course of the sample formation. It is shown that cooling a gas mixture is favorable to the clusterization of solute atoms in the gas flow. The krypton small clusters can serve as condensation clusters. The phase boundaries of the condensates have been determined. Regular Ar−Kr solutions are formed when the contents of one of the components are low (0−10 mol % Ar), (0−5 mol % Kr). The diffraction patterns of the condensates with prevailing Kr contents corresponded to a mixture of Kr-enriched fcc solutions and a dispersed phase of argon. The excess Kr contents are due to the specific morphology of the solutions dictated by condensation conditions. The Ar-based samples contained a mixture of two crystalline phases (an fcc solution and the hcp phase of nearly pure argon) and a glass phase of nearly pure krypton. In the concentration range 58−78 mol % Ar the new morphological form of the Ar−Kr condensates resembles the gel. The phase state diagram of the Ar−Kr condensates has been obtained.
In order to explain the anomalies documented in structure studies of dilute solid mixtures of argon in krypton, we calculated positions of atoms in a spheri-cal cluster of 9 layers. The interaction was approxi-mated by the Lenard-Jones potential. The respective substitution volumes ω have been evaluated. Our re-sults are compared with the generally accepted esti-mates obtained within the nearest-neighbor approxi-mation. We show that ω for the argon in krypton cluster is roughly twice as less than it follows from standard evaluations. This effect can be explained by the fact that the krypton atoms in the first coordination sphere feel an additional repulsion from their neigh-bors, which also tend to be closer to the center.
