Hydrogen Vibrations in Nickel Hydride
Nickel hydride was prepared in a BeCu high pressure cell at room temperature by applying a hydrogen gas pressure of 7kbar to pellets pressed from fine nickel powder. The rate and degree of completion of the hydride formation was first checked by neutron diffraction using deuterium gas with the result that a deuterium to metal ratio of approximately 0.75 was reached. After desorption of the deuterium, the nickel sample was charged with hydrogen for the inelastic incoherent neutron scattering measurements. Measurements were performed with the Be filter technique at the Brookhaven High Flux Beam Reactor. The optic modes appear as a broad band in the phonon density of states from about 70 to 110 meV with peaks at approximately 88 and 108 meV. Included in the discussion of these results will also be the effect of hydride formation on the acoustic phonon density of states.