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

HELIUM-VACANCY INTERACTION IN TUNGSTEN

The helium-decorated In-vacancy complex InV2Hen in tungsten was studied with the aid of the perturbed-angular-correlation technique, using In-111 as a probe. The release steps InV2Hen-->InV2Hen-1+He were identified for n=1-5. The corresponding dissociation energies are in the range of 2.9-4.5 eV, and agree perfectly well with the values determined by means of thermal-helium-desorption spectrometry. The quadrupole frequency is about 122 Mrad/s for n=1, 2 and about 101 Mrad/s for n=3,4 as compared to 133 Mrad/s for the undecorated In-vacancy complex (n=0). Trap mutation occurs when the vacancy is filled to an occupation number n congruent-to 10, and gives rise to a quadrupole frequency of 218 Mrad/s. Trap mutation ultimately leads to bubble formation. At least three different bubble-associated quadrupole interactions were observed