Quasielastic Neutron Scattering Study of Hydrogen Diffusion in C14-Type ZrMn2H3

1. Introduction Hydrogen diffusion in Laves-phase intermetallic compounds AB 2 shows a number of interesting features including high H mobility down to low temperatures, unusual isotope effects, and a coexistence of two frequency scales of H jump motion [1]. For the cubic (C15-type) Laves phases, the microscopic picture of H jumps and the systematics of the two frequency scales of H motion are well understood [1-3]. In most of the studied cubic Laves phases where H atoms occupy only tetrahedral interstitial sites of g type (A 2 BB 2), the faster jump process corresponds to the localized H motion within the hexagons formed by g sites, and the slower process (leading to long-range diffusion) is associated with H jumps from one g-site hexagon to another. The difference between the characteristic frequencies of these jump processes is believed to result from the difference between the g–g distances r 1 (within the hexagon) and r 2 (between the nearest hexagons). In contrast to the cubic Laves phases, the information on hydrogen diffusion in the hexagonal (C14-type) Laves phases is still fragmentary. The aim of the present work is to study the microscopic picture and the parameters of H jump motion in C14-type ZrMn 2 H 3 using quasielastic neutron scattering (QENS) measurements.