Diffusion of oxygen in silver

To explain the apparent deviation from Arrhenius dependence on temperature, T, of the diffusion coefficient, D, for oxygen atoms in silver, we invoke a quantum potential barrier crossing model. In this model, a harmonically localized O-atom annihilates a metal lattice phonon at the Debye frequency in order to gain enough energy to cross the potential barrier separating it from a neighboring site. Taking theta(D) = 225 K, for the Debye temperature of Ag, we fit the parameters of the model to experimental values of log D vs. 1/T, obtaining B = 620 meV and theta = 76 K, where B is the height of the barrier and theta is the Einstein temperature of the O-atom. The slightly concave down shape of log D vs. 1/T. is explained by the fact that theta < 2/3 theta(D). (C) 1999 Elsevier Science Ltd. All rights reserved.