An empirical potential for interstitial hydrogen in some C-15 Laves phase compounds from IINS measurements

Publisher Website
Google Scholar
Abstract
The potential wells seen by hydrogen in several interstitial sites in the C-15 Laves phase compounds, ZrTi2 (ZT), ZrCr2 (ZC) and TiCr1.85 (TC), have been investigated using incoherent inelastic neutron scattering (IINS) data. Parameters describing the harmonic terms in the H-potential well in the three compounds are obtained from the first localized hydrogen vibrations as measured by the IINS technique. The H-potential well is created by the sum of the pairwise potentials between the hydrogen and the four metallic atoms forming the different types of tetrahedral site which are labelled g (A2B2), e (AB3) or b (B4) in the C-15 structure. A Born-Mayer potential has been used to model these pairwise interactions, with parameters determined from the IINS. The resulting overall potential energy surface describes well the observed site occupancies and the diffusional behaviour of H in the ZC and TC compounds. On the other hand, due to the higher H content of the ZT sample, H-H interactions have to be included in the model for a proper description of the energy potential well in this compound. The potential energy surface enables us to identify the different diffusion paths of H in the C-15 structure and hence to infer the different time scales of H diffusion (localized and long-range diffusion) that have recently been shown to exist in these compounds (Skripov A V et al 1996 J. Phys.: Condens. Matter 8 L319-24; 1997 J. Alloys Compounds 253/254 432-4).