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| Book/Report | FZJ-2018-02702 |
1986
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18361
Report No.: Juel-2096
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 $Ti_{1.2}Mn_{1.8}D_{3}$ and $LaNi_{5}D_{7}$. In the latter case the dominant nickel scattering could be suppressed by isotope substitution with $^{60}$Ni, and the anisotropic broadening of the Bragg peaks could be modelled in a correspondingly modified Rietveld-profile refinement. For the investigatioln 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 intersitiols, transport jumps over the energetically higher sites and locally restricted jump processes. For $Ti_{1.2}Mn_{1.8}D_{3}$ the main features of the diffusional behaviour could be described quantitatively in the framework of a three state model. By means of neutron vibrational spectroscopy 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 $\alpha$-LaNi$_{5}$ H$_{x}$ La$_{2}$Ni$_{4}$%-octahedral and La$_{2}$Ni$_{2}$-tetrahedral interstitial sites are occupied. We have used the novel possibilities provided to neutron scattering by the new spallation sources in an investigation on $\beta$-V$_{2}$H. Using a unique single domain single crystal, for the first time the fundamental excitations 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 scatteringtechnique 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 spectroscopically determined ground state wave function.
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