Abstract
Vacancy-hydrogen interaction in molybdenum was investigated by means of the perturbed angular correlation technique, using the isotope In-111 as a probe. The complex InV2 turned out to trap up to two hydrogen atoms: trapping of a single hydrogen atom gives rise to a decrease of the quadrupole frequency by 3 Mrad s-1, whereas trapping of an additional hydrogen atom causes the frequency to increase by 5 Mrad s-1. Assuming a hydrogen migration energy of 0.35 eV, we 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. The lattice positions of the second hydrogen atom in molybdenum and tungsten are, therefore, completely different. Two more hydrogen decorated complexes were observed, with a binding energy of 1.07(3) eV. In the high-dose regime, a bubble-like feature was observed, the hydrogen binding energy being 0.72(3) eV.