GENERAL-THEORY OF INTERSTITIAL DIFFUSION IN CRYSTALS

A statistical mechanical theory of atomic diffusion in a crystal is developed with the assumption that tracer atoms with energies high enough to overcome the interstitial channel potential barrier epsilon can migrate in the entire lattice unless it is stopped by the lattice defects and the lattice vibrations. Combined with the results by means of a correlated walk model with trapping possibility, our theory establishes an Arrhenius law of diffusion: D equals D//o exp(-E//a/k//BT), with E//a equals epsilon and D//o equals (1/3) q* vl, where v, l and q* are, respectively, the migration speed, the mean straight path and a statistical weight ratio of order one. The theory is applied to N and C diffusion in alpha -iron.