Lattice dynamics of high-pressure hydrides of the group VI-VIII transition metals

Monohydrides of the group VI-VIII transition metals Cr, Mn, Fe, Co, Ni, Mo, Rh and Pd are synthesised under high hydrogen pressures and elevated temperatures and studied by inelastic neutron scattering (INS) at ambient pressure and low temperatures. In the measured INS spectra, the energy of the main optical H peak exhibits a strong monotonic increase as a function of the nearest hydrogen-metal distance in the hydrides of both 3d- and 4d-metals, respectively. The spectra for FCC NiH and PdH appear strongly anisotropic at energy transfers above the fundamental band of optical hydrogen vibrations, while those for FCC PdD do not show a significant directional dependence at energies of the second optical D band.