Hydrogen sites in amorphous Pd85Si15Hx probed by neutron vibrational spectroscopy

Abstract

In order to clarify the discrepancy between the Gaussian distribution of H-site energies suggested from different macroscopic measurements and the evidence for two energetically well separated types of H sites obtained from a microscopic H diffusion study by means of quasi-elastic neutron scattering, the authors have measured neutron vibrational spectra of hydrogen in amorphous Pd85Si15Hx, 0.13<or=x<or=8.23. At concentrations below 1% the spectra exhibit distinct features that indicate the occupation of distorted Pd6 octahedra, along with a range of tetrahedral sites. These observations are consistent with a bimodal distribution of H-site energies in this glassy metal hydride.