STRUCTURE STUDIES OF NE-H-2 SOLID-SOLUTIONS

We have carried out an x-ray study of solid parahydrogen-neon mixtures within the entire concentration range and at temperatures from 5 K to the respective solidus. The initial samples were prepared by depositi on from the gas onto a cool substrate. At low neon fractions x(Ne) we have found a number of anomalous phenomena: 1) the excess volume per i mpurity is a large positive value al a striking variance with Vegard's rule; 2) at low temperatures, two systems of hcp reflexes are observe d with lattice parameters close to those for the pure components; 3) t he increase in temperature up to the melting point results in that in alloys with x(Ne) > 0.25% both systems of reflexes simultaneously chan ge the symmetry to a fcc one, the fcc structure persisting on subseque nt temperature cycling. The above listed anomalies can be qualitativel y explained on the premise that the neon atom in the hydrogen lattice together with the nearest coordinate shell forms a metastable complex.