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MM: Fachverband Metall- und Materialphysik

MM 39: Computational Materials Modelling V

MM 39.10: Talk

Thursday, March 17, 2011, 18:30–18:45, IFW A

Superabundant vacancies in fcc metals: A combination of ab-initio, thermodynamic and kinetics approaches — •Roman Nazarov, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany

A dramatic increase of the vacancy concentration in a H-rich atmosphere, the so called superabundant vacancy formation, has been experimentally observed in several metals and alloys. In order to study this phenomenon we systematically applied density functional theory to a large set of fcc metals. We found that a large amount of H can be trapped by a monovacancy with, e.g., up to 15 H atoms in an Al vacancy, up to 12 H atoms in the case of Pd and more than 17 H atoms for Pb.

Based on the defect formation energies from DFT calculations, we have constructed a thermodynamic model that determines the equilibrium concentration of point defects as a function of temperature and H chemical potential. By applying this approach we revealed that the vacancy concentration can indeed strongly increase if H is added.

To understand the phenomenon of accelerated self-diffusion in a H-rich atmosphere we coupled the information on the number of vacancies from the thermodynamic treatment with self-diffusion barriers obtained from DFT calculations. Using this approach we found that the self-diffusion coefficient is reduced not only due to the increased vacancy concentration, but also as a result of a H-induced lubricant effect.