Structure and properties of solid parahydrogen-neon mixtures: influence of orthohydrogen and deuterium impurities

X-ray studies are performed on polycrystalline samples of mixtures of parahydrogen, orthodeuterium, and their normal modifications with neon over a wide range of concentrations and temperatures. The presence of an additional hcp phase having a lattice volume somewhat (0.5–0.7%) larger than the lattice volume of pure Ne is observed in all the systems except hexagonal and cubic mixtures with basic hydrogen-isotope and neon lattices. This new hexagonal phase is metastable and, when heated to premelting temperatures for hydrogen or deuterium, decomposes into the phases of the pure components. The additional hcp phase observed in the investigated systems is assumed to be formed by van der Waals complexes of the type Ne(H2)n or Ne(D2)n. The lattice parameters and molar volumes of the mixtures are determined. It is shown that impurities of hydrogen molecules with J = 1 have a weak influence on the miscibility and structural characteristics of the phases.