Neutron spectroscopy of nickel deuteride

A powder sample of fcc NiD synthesized under a deuterium pressure of 0.9 GPa at room temperature is studied at ambient pressure and 10 K by inelastic neutron scattering in the range of energy transfers 22-356 meV. The fundamental band of optical deuterium vibrations in NiD consists of a peak at 62 meV with a shoulder toward higher energies. The second and third optical bands demonstrate approximately harmonic behavior. The spectrum of NiD is similar to that of NiH compressed along the energy scale by a factor of r = 1.43(2) ≈ 2 characteristic of vibrations of D and H atoms in the same harmonic potential. Thermodynamic calculations using this value of r = 1.43 for optical vibrations in NiH and NiD accurately reproduce the experimental difference between the decomposition pressures of NiH and NiD near room temperature.