ISOTOPE DEPENDENCE OF HYDROGEN DIFFUSION IN METALS

Results of recent theoretical investigations about the isotope dependence of hydrogen diffusion in fee metals are reported which are based on a detailed analysis of multiphonon transitions beyond the Condon approximation. It is deduced that at high temperatures latticeactivated over-barrier transitions predominate (for Cu above about 150 K) whereas at lower temperatures quantum-mechanical tunneling transitions are of importance. Assuming an octahedral-tetrahedral-octahedral interstitial-site diffusion-path the theory yields for hydrogen diffusion in Cu the correct order of magnitude for the activation energy and is capable to describe the experimentally observed “inverse” isotope dependence. © by Akademische Verlagsgesellschaft