Mechanism for Self-Diffusion in Metallic Copper

The problem of the mechanism of diffusion in metallic copper is discussed from the standpoint of the modern theory of metals. Three competing processes are considered in detail, namely the mechanism of direct interchange of atoms, the mechanism of interstitial diffusion, and the mechanism of vacancy diffusion. The energies of the equilibrium and saddle-point configurations for the processes are determined first in an approximation in which the electronic charge distribution is assumed to be uniform throughout the lattice, and second in a further approximation in which polarization is taken into account by a simple variational method based on the one-electron scheme. The results indicate that the vacancy mechanism is strongly preferred and yield a value of the activation energy for diffusion in reasonable agreement with the observed one. The vacancy process is considered in greater accuracy in a paper by Huntington following this.