Crystal Structure of Solid Hydrogen and Deuterium, and of Neon—Hydrogen and Neon—Deuterium Mixtures

Abstract

Solid hydrogen (normal and para), deuterium, and the systems neon—hydrogen and neon—deuterium were studied by x-ray diffraction at various temperatures with and without prior plastic deformation. Under most conditions D2 freezes from the liquid phase as hexagonal close packed (hcp) and is stable in this form against plastic deformation; similarly H2 usually freezes in the hcp form. When gold foil with a cube texture is present, D2, normal H2 and para-H2 freeze in the face-centered-cubic (fcc) form. Plastic deformation at about 3° and 4.2° causes the addition of fcc reflections to the hcp diffraction pattern with samples of normal H2 that previously had shown only hcp. It is concluded that normal H2 is metastable in the hcp structure at these temperatures, and that the spontaneous transformation to cubic on cooling may often be incomplete. It was found that, in concentrations between 0.25% and 99.5% Ne, Ne and the hydrogens are immiscible.