Al effect on the local structure of high entropy alloys and related hydrides

Metal hydrides of intermetallics/alloys are proposed as safe and efficient solid-state hydrogen storage materials. In this context, we are currently studying high entropy alloys containing refractory elements and Al, as an agent to alter the thermodynamics of the reaction with hydrogen. However, this thermodynamic tunability occurs at the expenses of the storage capacity, which decreases steadily with Al content. A clear explanation of the underlying mechanism of this capacity fading is still missing. Possible reasons might be cited: short-range ordering and strong lattice distortion in the presence of Al, pairing of Al-d metal atoms, clustering of Al atoms etc. Thus, we propose to study here the local structure of several promising high entropy alloys and its evolution during the first H absorption/desorption by in situ X-ray total scattering and associated PDF analysis. This will help the design of high-capacity alloys with tuneable thermodynamics.