NEUTRON SPECTROSCOPIC COMPARISON OF RARE-EARTH HYDROGEN ALPHA-PHASE SYSTEMS

incoherent inelastic neutron scattering was used to study the vibratio nal spectroscopy of hydrogen (and deuterium) in alpha-phase solid solu tion with Sc, Lu, and Y. Low-resolution spectra of the tetrahedrally-b ound H (and D) in the three rare-earth metals exhibit similar behavior : a soft c-axis-polarized vibration approximately 25 - 30% lower in en ergy than the doubly-degenerate vibrations polarized along the basal p lane. Previous diffuse elastic neutron scattering studies of these sys tems indicate the existence of short-range ordering of metal-atom-brid ged hydrogen pairs into c-axis directed chains. High-resolution spectr a of the broad c-axis vibrations reveal a temperature- and H-concentra tion-dependent splitting believed to represent local ''optic'' and ''a coustic'' bands associated with the dynamical coupling of these hydrog en pairs. The shape and width of these bands at low temperature near t he alpha/beta-phase boundary vary among the three metals, becoming sha rper in the order of increasing atomic volume (Sc-->Lu-->Y), and sugge sting an increasing extent of short-range order of hydrogen pairs.