NEUTRON-SCATTERING STUDIES OF THE STRUCTURE AND DYNAMICS OF THE PDCU-H ORDERED PHASE PRODUCED UNDER A HIGH HYDROGEN PRESSURE

An atomically ordered PdCuH almost-equal-to 0.9 hydride was synthesize d at 600 K and a hydrogen pressure of 3 GPa. Its metal lattice had a p rimitive tetragonal cell formed from the initial FCC cell of the disor dered PdCu alloy due to ordering of the Pd and Cu atoms into alternate layers perpendicular to the tetragonal c-axis. Rietveld refinement of the neutron diffraction pattern of PdCuH almost-equal-to 0.9 measured at 80 K showed the H atoms to occupy octahedral interstitials within the Pd layers. The inelastic neutron scattering study at 35 K revealed a broad hydrogen optical peak with peculiarities at energy transfers of 79 and 95 meV and of 113 meV which were ascribed to the H vibration s in the Pd-H planes and along the Cu-H chains perpendicular to the pl anes, respectively. The potential for hydrogen atoms in the PdCuH almo st-equal-to 0.9 ordered phase was thus noticeably different, even in t he Pd-H plane, from that in the known hydrides of palladium and pallad ium alloys. The value of approximately 116 meV was predicted for the l ocal H vibrations in dilute Cu-H solid solutions.