Tracer correlation factor and atomic displacements due to the collinear interstitialcy mechanism

Abstract

It is shown that the tracer correlation factor for diffusion by the collinear interstitialcy mechanism, in the limit of low defect concentrations, has the simple general form f = 1 − 1/(Z′ − 1), where Z′ is the number of nearest neighbour normal lattice sites to an interstitial site. This result is obtained by deriving expressions for the atom jump probabilities from random walk theory. These jump probabilities also enable the atomic displacement probabilities due to a single atom-defect encounter to be obtained in the form of an integral expression. The theory is applied to diffusion in the NaCl structure as an example.