The formation of super-abundant vacancies (vacancy–H clusters) was studied in Nb–H alloys by means of resistivity measurements as a function of temperature, pressure and H concentration. The formation energy of a vacancy–H cluster (0.3eV), which was 10% of the formation energy of a vacancy, was explained tentatively as being the result of six H atoms which were trapped by a vacancy with an average binding energy of 0.46eV/H-atom. The super-abundant vacancies were introduced from the external surface, and were transported into the interior by direct bulk diffusion and/or by fast diffusion along dislocations. The activation volumes for the formation and migration of vacancy–H clusters were 3.7 and 5.3Å3, respectively.

Super-Abundant Vacancy Formation in Nb–H Alloys - Resistometric Studies. H.Koike, Y.Shizuku, A.Yazaki, Y.Fukai: Journal of Physics - Condensed Matter, 2004, 16[8], 1335-49