Hydrogen-vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope '"In as a probe.Hydrogen trapping at an "'In-vacancy cluster manifests itself as a change of the locd electric field gradient, which gives rise to an observable shift of the quadrupole frequency. The measurements show that a vacancy in tungsten can trap one or two hydrogen a t o m at room temperature. The detrapping energies of the first and second hydrogen atom are 1.55(2) and 1.38(2) eV, mpectively, while the detrapping enof the next hydrogen atom is less than 1.1 eV. Substitutional " ' I n atoms do not trap hydrogen at room temperature. At least two more hydmga decorated defects were observed. Although their StmctureS are not quite clear, they probably fonn from larger vacancy clusters and may eontain a large amount of hydrogen. The dissociation energy of these bubble-like defects is 1.30(2) eV.
Vacancy-hydrogen interaction in molybdenum was investigated by means of the perturbed angular correlation technique, using the isotope 111In as a probe. The complex InV2 turned out to trap up to two hydrogen atoms. Assuming a hydrogen migration energy of 0.35 eV, the authors found the binding energies of the first and second hydrogen atoms to be 1.07(3) eV and 0.44(3) eV, respectively, while the binding energy of the next hydrogen atom is <0.25 eV. The sign of the frequency shift due to the second hydrogen atom trapped at InV2 is opposite to that recently observed in tungsten, and the dissociation energy is much smaller.
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