In order to study the mechanism and parameters of H diffusion in the cubic (C15-type) Laves phase, YMn2, quasi-elastic neutron scattering measurements were performed on YMn2Hx (x = 0.4, 0.65 and 1.26) at 30 to 395K (figure 5). It was found that the diffusive motion of H in this system could be described in terms of two jump processes: the fast localized H motion with the jump rate τl-1 and the slower process with the rate τd-1 associated with H jumps leading to long-range diffusion. The ratio τd /τl at room temperature was close to 102. The results suggested that the localized H motion in YMn2Hx corresponded to back-and-forth jumps of H atoms within pairs of interstitial g (Y2Mn2) sites. The parameters of the long-range diffusion of H in the samples with different H content were found to be close to each other. In the range 210–395K, the temperature dependences of τd-1 and the H diffusivity were reasonably described by the Arrhenius law with activation energies of 0.18 to 0.22eV.

Quasi-Elastic Neutron Scattering Study of Hydrogen Motion in C15-type YMn2Hx. A.V.Skripov, J.C.Cook, T.J.Udovic, M.A.Gonzalez, R.Hempelmann, V.N.Kozhanov: Journal of Physics - Condensed Matter, 2003, 15[21], 3555-66

Figure 5

Tracer Diffusivity of H in Mn2Y

(Circles: Mn2YH0.4, triangles: Mn2YH0.65, squares: Mn2YH1.26)