Neutronenstreuung an Hydriden intermetallischer Verbindungen

Abstract

This review surveys the application of neutron scattering for the investigation of the microscopic behaviour of hydrogen in intermetallic compounds. This concerns the structure as well as the dynamics. Neutron diffraction experiments were performed on Ti, Mn. 0D and LaNi D-,. In the latter case the dominant nickel scattering could be suppressed by Isotope Substitution with Ni, anc [the anisotropic broadening of the Bragg peaks could be modelled in a correspondingly modified Rietveld-profile refinement. For the investigation of hydrogen diffusion in intermetallic hydrides by means of quasielastic neutron scattering an iterative multiple scattering correction procedure has been developped which allows a reliable determination of hydrogen diffusion coefficients. The mechanism of hydrogen diffusion in intermetallic hydrides comprises three types of jumps: escape jumps out of energetically lower interstitials, transport jumps over the energetically higher sites and locally restricted jump processes. For Ti Mn, H the 1. Z 1. o j main features of the diffusional behaviour could be described quantitatively in the framework of a three State model. By means of neutron vibrational spectr'oscopy Information about the occupied hydrogen sites and thus about the structure can be extracted from the symmetry Splitting of the vibrational modes. In this way we showed that in a-LaNi H La Ni,-octahedral and La Ni.-tetrahedral interstitial sites are occupied. 2 4 2 2 r We have used the novel posslbilities provided to neutron scattering by the new spallation sources in an investigation on ß-V2 H. Using a unique Single domain Single crystal, for the first time we determined the directions of the fundamental excitations of a hydrogen atom in a metal. Overtones of these vibrations were observed up to 14th order. They establish a well defined H potential up to more than 1 eV. The sequence of excitations could be described quantitatively in terms of an empirical potential. Using the same sample we have also performed the first neutron Compton scattering experiment on a metal hydride. With this novel neutron scattering technique the momentum distribution and therefore - at low temperature -the ground State wave function is measured. The thus determined kinetic hydrogen energy is in good agreement with that calculated from the spectro scopically determined ground State wave function.