NEUTRON-SCATTERING STUDIES OF ORDERED PDCUH AND PDAGH PREPARED UNDER A HIGH HYDROGEN PRESSURE

Atomically ordered PdAgHx and PdCuHx hydrides with x approximate to 0. 9 were synthesized in an atmosphere of gaseous hydrogen at P = 3 GPa. Their metal lattices with primitive tetragonal cells were formed on th e basis of fee lattices of the initial PdAg or PdCu disordered alloys due to the ordering of the Pd and Ag or Cu atoms into alternate layers perpendicular to the tetragonal c-axis. Rietveld refinement of the ne utron diffraction pattern of the PdCuHapproximate to 0.9 measured at 8 0 K, showed the H atoms to occupy octahedral interstitials within the Pd layers. The inelastic neutron scattering study of PdCuHapproximate to 0.9 and PdAgHapproximate to 0.9 showed a large difference between t he Pd-H, Cu-H and Ag-H interactions. Values of 93 and 116 meV were pre dicted for the local H vibrations in dilute Ag-H and Cu-H solid soluti ons.