Hydrogen-induced nonmonotonic hopping structure evolution in Pd-based alloys

We show that the nonmonotonic discrete (“hopping”) structure evolution takes place in nonequilibrium Pd-based alloys after hydrogen charging. It can be explained by assuming the thermodynamic potential to be of multivalley form. The states of the system corresponding to these valley minima are long-lived states. The system hops between the long-lived states during the structural evolution due to the cooperative migration of hydrogen and vacancies between matrix and defect regions. The experimental results show that such jumps can cause the lattice period to increase or decrease.