Theory of incoherent hydrogen diffusion in metals

Hydrogen migration in a one-dimensional model of the bcc lattice is examined using the double-time Green functions, for temperatures at which the migration mechanism is mainly due to the thermally activated tunnelling of a proton. In deriving the coefficient of incoherent hydrogen diffusion, allowance is made for the lattice distortion around the hydrogen and for the two-phonon scattering processes. It is shown that the observed temperature break in the activation energy of incoherent hydrogen diffusion in bcc metals is the result of the change in the mechanism responsible for an elementary diffusion process near the Debye temperature, anmely, it is the result of the transition from “passive” to “active” transport.