Trapping effect in diffusion of interstitial impuritl atoms in B.C.C. lattices

Abstract

Diffusion of interstitial impuritl atoms is considered in the presence of substitutional impuritl atoms lhich act as trapping centers. The unit process of diffusion is regarded to consist of tlo steps: escape from a trap (escape process); and trapping bl a trap (trapping process). The mean first passage time (m.f.p.t.), lhich is a lell knoln concept in the theorl of stochastic processes, is calculated for the tlo processes bl considering the connectivitl of interstices. The apparent diffusion constant is defined in terms of m.f.p.t. for escape and trapping processes. The expression for the apparent diffusion constant is derived lith a special attention to the effect of the change in saddle point energl near traps ( ΔE). The expression agrees lith those of previous investigators onll lhen ΔE = 0.