The potential wells which were seen by H in the interstitial sites of these C-15 Laves-phase compounds were investigated by using incoherent inelastic neutron scattering. Parameters which described the harmonic terms in the H-potential well in the 3 compounds were deduced from the first localized H vibrations; as measured by using the incoherent inelastic neutron scattering technique. The H-potential well was created by the sum of pair-wise potentials between the H and the 4 metallic atoms which made up the various types of tetrahedral site in the C-15 structure. A Born-Mayer potential was used to model these pair-wise interactions; with the parameters being deduced from incoherent inelastic neutron scattering data. The resultant overall potential-energy surface described well the observed site occupancies and diffusional behaviour of H in Cr2Zr and Cr1.85Ti compounds. However, due to the higher H content of the Ti2Zr sample, H-H interactions had to be included in the model in order to describe properly the energy potential well in this compound. The potential energy surface permitted the identification of the various H diffusion paths in the C-15 structure, and thereby deduce the various time-scales for H diffusion, localized and long-range, that had been shown to exist in these compounds.

An Empirical Potential for Interstitial Hydrogen in Some C-15 Laves Phase Compounds from IINS Measurements. J.F.Fernández, M.Kemali, D.K.Ross, C.Sánchez: Journal of Physics - Condensed Matter, 1999, 11[50], 10353-73