Vacancies and Self-Interstitials

Conclusions

This article has traced the concept of vacancy diffusion, starting with the Kirkendall effect through various stages to present universal acceptance as the preferred mechanism for impurity and self-diffusion for most metals and insulators. For pure metals we expect the activation energy for self-diffusion to be the sum of the energy for vacancy formation and the energy of motion but for impurity diffusion the temperature dependence of the correlation effect will make a contribution. Because of its large formation energy, the self-interstitial is not a thermal defect, but it does play a dominant role in the low-temperature annealing of radiation-damaged specimens. Large-scale computer calculations have been important in exploring both the process of displacement generation and the subsequent history of the interstitialcy as it moves in diffusion. In the guise of a crowdion the interstitial can be expected to have a long free path, but it is more stable in the dumbbell mode.