Role of the local structure on the hydrogen reaction pathway of high entropy alloys

Among several materials currently proposed for safe and efficient solid-state hydrogen storage, alloys and intermetallics are some of the most promising candidates due to high volumetric capacities and chemical tuneability. We are currently studying the bcc TiZrNbHfV1-xTax (x = 0, 0.25, 0.5, 0.75 and 1) high entropy alloys forming high-capacity hydrides. Despite the same initial bcc lattice and close chemical composition (80%), the phase transition pathway during the reaction with gaseous H is different: H absorption in the TiZrNbHfV alloy occurs in a one-step reaction directly forming a dihydride, while when V is even partially substituted by Ta in TiZrNbHfV1-xTax that induces a two-step transformation via an intermediate monohydride. It is unclear which parameters influence this phase transformation: electronic properties, local structure, or lattice strain. Thus, we propose to clarify here the local structure in the various deuteride phases in this series of alloys by ex-situ total neutron scattering and associated PDF analysis. This will help in understanding the reaction pathway with hydrogen/deuterium at local level and improving the design of high-capacity materials.