A MODEL FOR THE CALCULATION OF MONOVACANCY AND DIVACANCY CONTRIBUTIONS TO THE IMPURITY DIFFUSION IN NOBLE-METALS

The impurity diffusion in noble metals is described taking into account the contribution of divacancies. The influence of the divacancy contribution on the effective diffusion energy and on the temperature dependence of the isotope effect is discussed. The divacancy contribution causes a curvature of the Arrhenius plot of the diffusion coefficient. For fast diffusing impurities the temperature behavior of the correlation factor f leads to a distinct decrease of this curvature. A further consequence of the temperature behavior of f for fast diffusers is that the low-temperature value of DELTA Q, the difference between the activation energies of impurity diffusion and self-diffusion, represents an acceptable upper limit for the binding energy between impurity and vacancy.