Low-temperature isotope effect of hydrogen diffusion in f.c.c. metals and alloys

Abstract

Abstract Abstracy Magnetic after-effect measurements of hydrogen and deuterium in f.c.c. binary alloys at low temperatures have shown that the values of the pre-exponential factor, v o, are a factor of 10–105 too small compared to those expected for a classical diffusion process. Furthermore, a comparison between high-and low-temperature diffusion reveals a significant deviation from an. Arrhenius-type behaviour. These deviations are more pronounced for the H than for the D isotope and seem to be a common feature of all f.c.c. metals. Recent quantum-mechanical investigations of the diffusion of light particles in f.c.c. metals, in particular Cu, can account qualitatively for the observed temperature dependence of the diffusion coefficient and for its isotope effect and relate it to a competition between over-barrier and tunnelling transitions of the H isotopes. At high temperatures diffusion takes place almost exclusively by over-the-barrier transitions, whereas with decreasing temperature and, particular...