Neutron scattering studies of ordered PdCuH and PdAgH prepared under a high hydrogen pressure

Atomically ordered PdAgHx and PdCuHx hydrides with x 0.9 were synthesized in an atmosphere of gaseous hydrogen at P = 3 GPa. Their metal lattices with primitive tetragonal cells were formed on the basis of fcc 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 neutron diffraction pattern of the PdCuH0.9 measured at 80 K, showed the H atoms to occupy octahedral interstitials within the Pd layers. The inelastic neutron scattering study of PdCuH0.9 and PdAgH0.9 showed a large difference between the Pd-H, Cu-H and Ag-H interactions. Values of 93 and 116 meV were predicted for the local H vibrations in dilute Ag-H and Cu-H solid solutions.