Abstract
The formation of superabundant vacancies (SAVs; vacancy–hydrogen clusters) wasstudied in Nb–H alloys by means of resistivity measurements as a function oftemperature, pressure and H concentration. The formation energy of a vac–H cluster(0.3 ± 0.1 eV),which is 1/10 of the formation energy of a vacancy in Nb, is explained tentatively as being theconsequence of six H atoms trapped by a vacancy with the average binding energy of0.46 eV/H atom. The SAVs were introduced from the external surface, and transported into theinterior by direct bulk diffusion and/or by fast diffusion along dislocations. The activationvolumes for the formation and migration of vac–H clusters were determined to be 3.7 and5.3 Å3, respectively.
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