Recovery of Electron-Irradiated Copper. II. Interstitial Migration

Several experiments are presented dealing with substages ${\mathrm{I}}_D$ and ${\mathrm{I}}_E$ of Stage I (14°K-65°K) recovery in electron-irradiated pure copper. It is concluded that both ${\mathrm{I}}_D$ and ${\mathrm{I}}_E$ represent the recovery due to the free diffusion of a defect, presumably an interstitial atom, with an activation energy for motion $E_m=0.12\mathrm{}\pm 0.005$ ev. ${\mathrm{I}}_D$ is the result of correlated recovery (the interstitial returns to the vacancy from which it came) while ${\mathrm{I}}_E$ is the result of uncorrelated recovery (the interstitial travels to a distant sink). The migrating interstitial is shown to interact with vacancies, traps, and other interstitials leading respectively to annihilation, trapping, and cluster formation. The interaction between two interstitials leading to cluster formation is found to be comparable with the annihilation interaction between an interstitial and a vacancy. Clusters containing more than two interstitials are also formed. Previous work in copper is discussed, and it is concluded that this previous work is consistent with the above description of Stage I recovery. The relationship of the present work to the general problem of assigning defect processes to the higher temperature recovery states in copper is also discussed.