Underlying factors of mega pressure hysteresis in cerium-rich CaCu₅-type metal hydrides and effective modification strategies

To unmask the ambiguous underlying factors responsible for the mega pressure hysteresis in Ce-rich CaCu5-type metal hydrides, (La-Ce)-Ni binary and ternary alloys are chosen as the research objects for systematic investigations. It's worth mentioning that CeNi5 possesses an extreme hysteresis factor of 1.98 with hydrogenation equilibrium pressure that is 134 times higher than that of LaNi5. By characterization, the relevant potential triggers for Ce-related mega pressure hysteresis and outrageous hydrogenation differences can be categorized into the following two aspects. On the one hand, the strong elastic deformation resistance and the generated significant deformation energy accumulation will noticeably hinder the hydrogenation deformation process. On the other hand, the intrinsic Ce-based stable energetic state and valence bonding may also contribute to the exceptional difficulty in disrupting the original stable ground state. Fortunately, composition engineering realized through convenient hydride precipitation and staged phase transformation are proven to be the most effective in ameliorating the mega pressure hysteresis in Ce-rich metal hydrides. Overall, the relevant findings here will pave the way for better understanding and amelioration of the pressure hysteresis of metal hydrides.