Structures studies of Ne–H2 solid solutions

Solid parahydrogen–neon mixtures are subjected to x-ray structure analysis over the entire range of concentrations at temperatures varying from 5 K to the solidus temperature. The initial samples are obtained by condensation from the gaseous phase on a cold substrate. At low concentrations xNe of neon, a number of anomalous phenomena are observed: (1) excess volume per impurity turns out to be large and positive, which is in contradiction with Vegard’s rule; (2) at low temperatures, two systems of hcp reflexes are observed with lattice parameters close to corresponding values for the pure components, and (3) an increase of temperature to the melting point of the alloy with xNe>0.25% leads to a simultaneous change in the symmetry of both systems of reflexes to that of fcc structure which is preserved upon a further temperature cycling. These anomalies can be explained qualitatively by assuming that a neon atom in the hydrogen lattice forms a single metastable complex with the nearest coordination sphere.

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