HYDROGEN VACANCY INTERACTION IN TUNGSTEN

Hydrogen-vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope In-111 as a probe. Hydrogen trapping at an In-111-vacancy cluster manifests itself as a change of the local 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 atoms at room temperature. The detrapping energies of the first and second hydrogen atom are 1.55(2) and 1.38(2) eV, respectively, while the detrapping energy of the next hydrogen atom is less than 1.1 eV. Substitutional In-111 atoms do not trap hydrogen at room temperature. At least two more hydrogen decorated defects were observed. Although their structures are not quite clear, they probably form from larger vacancy clusters and may contain a large amount of hydrogen. The dissociation energy of these bubble-like defects is 1.30(2) eV.