Effects of hydrogen ordering on the vibrational spectra of H(D) in HfV 2H4−yDy

The vibrational spectra of H(D) in C15-type HfV 2H4.0, HfV 2D4.0 and HfV 2H1.5D2.5 have been studied by means of inelastic neutron scattering above and below the temperature of H(D) ordering. It has been found that the hydrogen order-disorder transition leads to significant changes in the shape of the hydrogen vibrational spectra. These changes can be attributed (at least, partially) to a redistribution of hydrogen atoms between the interstitial sites with HfV 3 and Hf2V 2 coordination. The experimental data for the disordered phase of HfV 2H4(D4) are consistent with the considerable isotope effect on the occupancy of the HfV 3 sites by H(D) atoms.