Neutron energy-loss measurements from ZrCoH(D)x

Abstract

Neutron inelastic scattering has been used to investigate the system ZrCoH_x for x=0.6, 1.2 and 2.4. It is first shown that, in the harmonic approximation, the areas of peaks due to the optical vibrations of hydrogen atoms, when measured on a Be filter spectrometer, are, to a good approximation, proportional to the number of hydrogen atoms in the corresponding site times the degeneracy of the mode in question. The experimental results show that the hydrogen atoms in ZrCoH_x have optical mode vibrations in the range 90-180 meV. All the measured spectra are accounted for by five gaussian peaks, and two of these are common to all three samples. Two of the samples are in that alpha + beta ₁ phase field by the areas of the gaussian peaks increase closely in proportion to the total hydrogen content of the samples. While similar, the single-phase sample (x=2.4) shows some significant differences in the peak distributions. Making reference to neutron diffraction results and Westlake's criteria (1980, 1982) for the size and separation of hydrogen sites, a tentative assignment of frequencies and lattice sites is made. This is compared with similar results for the system ZrNiH_x.