Hydrogen motion in near stoichiometric yttrium dihydride at elevated temperatures

The high -temperature motion of hydrogen in near stoichiometric yttrium dihydride (YHx, x = 1.62 and 1.87 at. %) was investigated using incoherent quasi -elastic neutron scattering and Density Functional Theory (DFT) calculations as a function of hydrogen stoichiometry. Translational motion (diffusivity) of hydrogen in yttrium dihydride was only observed in a temperature range of 1073-1173 K under vacuum environment. The hydrogen motion was found to be limited to the tetrahedral sublattice, and diffusivity of hydrogen was observed to increase with decreasing hydrogen stoichiometry. The same behavior was also supported with DFT calculations. The DFT results also indicated that certain migration paths with smaller energy barriers favored H jump resulting in higher diffusivities.