Vibration Spectra of Vanadium Hydride in Three Crystal Phases by Inelastic Neutron Scattering

Abstract

The vibration spectra of vanadium hydride in three crystal phases have been investigated by the energy‐gain scattering of cold neutrons. The measured spectra are generally split into two broad bands above and below about 300 cm− 1, which are primarily associated with optical hydrogen vibrations and metal‐atom vibrations, respectively. Pseudofrequency distributions for the hydrogen vibrations were derived from the measuredneutron spectra. These indicate broad optical vibration bands peaked at 970 ± 50 and ∼1400 cm− 1 in the α (bcc) phase, 440 ± 20, 970 and ∼1400 cm− 1 in the β (bct) phase, and ∼1300 cm− 1 in the γ (fcc) phase. The width of the 440‐cm− 1 band increases with hydrogen concentration, possibly due to hydrogen–hydrogen interactions. The “metal‐atom” vibration spectra also show changes in peak positions and widths as the distribution of phases is changed. The changes in the neutron spectra with temperature and as a function of composition between VH0.20 and VH1.71 correlate quite well with the previously measuredphase diagram. A comparison of the present results with neutron spectra for hydrides with known hydrogen positions suggests that in the α phase hydrogens only occupy tetrahedral‐type sites, while in the β phase both octahedral and tetrahedral sites are occupied. The results for VH1.49 and VH1.71 indicate that in the γ phase the hydrogens occupy regular tetrahedral sites corresponding to the fluroine positions in a CaF2‐type structure.