In situ hydrogen sorption in high entropy alloys: role of the local structure on the reaction pathway

Among several materials proposed for safe and efficient solid-state hydrogen storage, alloys and intermetallics are the most promising candidates. We are currently studying the series of bcc (TiZrNbHf)80V20-xTax (x = 0, 5, 10, 15 and 20) 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 H is different: H absorption in V-rich and Ta-rich alloys shows one and two-step reaction, respectively. However, it is not clear yet, which parameters influence this phase transformation: electronic properties, local structure, or lattice strain. Thus, we propose to study here the phase transformation at local level in this series of alloys during the first H absorption/desorption by in situ X-ray total scattering and associated PDF analysis. This will help understanding the H absorption pathway at local level for further design of high-capacity materials.