Ring diffusion in metals

Abstract

The concept of hole migration in metals as the mechanism of self-diffusion and of diffusion of substitution-solute atoms has arisen from the apparent failure of other reasonable mechanisms, such as direct interchange, to give heats of activation comparable to those observed. In the present paper it is pointed out that diffusion by direct interchange is only a special case of diffusion by the synchronized cychc motion of a number of atoms, herein called ring diffusion. General arguments are presented demonstrating that a 4-ring has a lower potential-energy barrier for cyclic motion than has a 2-ring, which corresponds to direct interchange. These general arguments are supported by detailed calculations for the particular case of self-diffusion in copper. It is concluded that such ring diffusion is not excluded by energy considerations.