The role of impurity oxygen in hydrogen bubble nucleation in tungsten

The impurity role for hydrogen bubble nucleation is investigated based on first-principles studies of the interaction between impurities (oxygen and carbon), hydrogen and vacancy in tungsten. A new mechanism of hydrogen bubble nucleation is proposed: the interstitial oxygen atom traps multiple hydrogen atoms inducing the appearance of some unstable lattice sites nearby, where the initial vacancy can be created to form vacancy–oxygen–hydrogen complex, whose formation energy is so low that abundant vacancy–oxygen–hydrogen complexes could survive and thus the hydrogen bubble nucleates. This mechanism could provide a sound explanation for the hydrogen bubble nucleation in tungsten (with quite low vacancy concentration) exposed to low-energy (far lower than displacement threshold energy) deuterium ions irradiation. The proposed mechanism should be generally applicable for hydrogen bubble nucleation in other metals with low vacancy concentration.