J. M. Rowe

Direct determination of the anharmonic vibrational potential for H in Pd

The vibration spectra of α and β-phase PdH(D)x have been measured by neutron inelastic scattering. From a detailed analysis of the spectra, we conclude that the potentials for hydrogen and deuterium are very similar and strongly anharmonic. The results show definitively that anharmonicity is the principal contribution to the anomalous isotope dependence of the superconducting transition temperature in PdH(D).

Localized hydrogen modes in LaNi5Hx

Abstract The localized vibrations of hydrogen in various LaNi5Hx samples were studied using inelastic neutron scattering (neutron spectroscopy). The pronounced vibrational peaks obtained for “virgin” strain-free α-LaNi5H0.15 indicate the existence of two different hydrogen sites. During the activation for hydrogen absorption, substantial distortion is introduced into the LaNi5 lattice which is locally probed by the vibrating hydrogen atoms.

Hydrogen site distribution in the alloy system Nb100 − xVxHy studied by neutron vibrational spectroscopy☆

Abstract Nb 100 − x V x H y is a random b.c.c. alloy with a hydrogen sublattice disordered with respect to site energies. We have determined the energetically most favourable hydrogen sites by means of neutron vibrational spectroscopy, which is a powerful tool for this purpose when the translational symmetry is strongly reduced. In Nb 95 V 5 H y , Nb 90 V 10 H y and Nb 50 V 50 H y both octahedral and tetrahedral site occupation was observed. On the basis of spectroscopic and statistical arguments we assign the low temperature vibrational peaks in the niobium-rich NbVH alloys at low hydrogen content to Nb 4 V 2 octahedral and NbV 3 tetrahedral sites.

Localized Vibrations of Hydrogen in Metals

We report inelastic neutron scattering experiments on H and D in β-TaH0.5 and Nb99Ti1H(D)1. On TaH0.5 higher harmonics of the hydrogen vibrations were found up to 400 meV. Qualitatively the observed anharmonicity agrees with recent ab initio frozen phonon calculations on NbH. Spectroscopic results on the impurity system NbTiH(D) allow for the first time a determination of the H-potential for a dilute metal-H- system. The observed anharmonicity is twice as large as in a corresponding hydride phase.

Influence of Substitutional and Interstitial Impurities on Local Hydrogen Modes in Nb

Neutron vibrational spectroscopy has been used to study the association of H with interstitial (O) and substitutional (V) defects in a Nb host. From these results we propose a model for the site occupancy of H bound by O at low temperatures.