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MM: Fachverband Metall- und Materialphysik

MM 47: SYM Hydrogen in Materials: New Developments V

MM 47.5: Vortrag

Freitag, 29. Februar 2008, 11:35–11:55, H 1058

Hydrogen interaction with vacancies studied by positron annihilation — •Jakub Cizek — Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic

Vacancies as open-volume defects provide an additional space in lattice which makes them attractive for hydrogen. Trapping of multiple hydrogen atoms in vacancies was observed in metals. Hydrogen is not only trapped at vacancies existing already in the material, but new vacancies may also be created by hydrogen loading. Positron annihilation spectroscopy (PAS) is a well-developed non-destructive technique with very high sensitivity to open-volume defects, in particular vacancies. Type of defects and defect densities can be determined using PAS. Thus, PAS is an ideal tool for investigations of hydrogen interactions with vacancies. This contribution reports about defect studies of bulk Nb and Pd specimens step-by-step loaded to various hydrogen concentrations. PAS studies were combined with X-ray diffraction and TEM investigations. The experimental data were compared with theoretical calculations of energetic stability and positron characteristics of various defect-hydrogen configurations. We have found that vacancy-hydrogen complexes are introduced into the specimens by hydrogen loading. Density of these vacancy-hydrogen complexes increases with increasing concentration of hydrogen in the specimens. Additional defects are introduced at higher hydrogen concentrations due to precipitation of hydrides. Another type of vacancy-hydrogen complexes can be introduced by electron irradiation. Configuration, stability, and mechanism of formation of the hydrogen-induced defects are discussed.