Phase separation in nH sub(2)-nD sub(2) alloys

Using powder x-ray technique we have studied the structure of solid mixtures of normal hydrogen and deuterium nH sub(2)-nD sub(2), the samples being prepared by deposition from the gas onto a substrate at a temperature near 5 K. The content of nD sub(2) in the alloys was varied from 0 to 100%. Over...

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Bibliographic Details
Published in:Journal of low temperature physics 1999-01, Vol.115 (3), p.109-126
Main Authors: Strzhemechny, M A, Prokhvatilov, A I, Shcherbakov, G N, Galtsov, N N
Format: Article
Language:English
Subjects:
Binary mixtures
Composition effects
Deuterium
Hydrogen
Phase diagrams
Phase equilibria
Phase separation
Thermal effects
X ray crystallography
X ray powder diffraction
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Summary:Using powder x-ray technique we have studied the structure of solid mixtures of normal hydrogen and deuterium nH sub(2)-nD sub(2), the samples being prepared by deposition from the gas onto a substrate at a temperature near 5 K. The content of nD sub(2) in the alloys was varied from 0 to 100%. Over the range 20 to 85%, the diffraction patterns contain two sets of hcp reflections, which correspond to phases rich in hydrogen and deuterium. As the temperature was raised to 12-14 K (depending on the composition), the separated alloys with comparatively fine crystallites started to show indications of growth and, simultaneously, homogenization, sometimes to completion. These states remained stable upon subsequent decreases in temperature. Analysis of the data supports the claim that phase separation occurs in nH sub(2)-nD sub(2) alloys during sample preparation. This result confirms the finding by Kogan, Lazarev, and Bulatova. The characteristic points (kinks on the molar volume vs. composition, the position of the boundary of the homogenization area, etc.) are treated as belonging to lability rather than equilibrium lines. Proceeding from these arguments we reconstruct a hypothetical phase diagram which has the maximum separation temperature T sub(c) within the range 8-11 K. As shown using a model, which accounts for the electrical quadrupole (EQQ) interaction between J identical with 1 species, the T sub(c) is substantially higher than predicted by Mullin and Sarin. We suggest some explanation for the striking difference between the results of different studies carried out to search for phase separation in solid mixtures of deuterium and hydrogen on samples prepared by different methods.
ISSN:0022-2291