Multiple hydrogen occupancy of vacancies in Fe

The binding of multiple deuterium (D) atoms to vacancies in iron (Fe) is investigated both experimentally, by use of ion-beam techniques, and theoretically, by use of the effective-medium scheme. The experimental D-release stages are accounted for by trapping at vacancies with a binding enthalpy that depends on occupancy. It is found that for 1-2 D in a vacancy, the trap strength is 0.63 eV, whereas the binding enthalpy for 3-6 D in a vacancy is 0.43 eV. These results are in good agreement with predictions from the effective-medium theory.