Anelastic relaxation due to single self-interstitial atoms in electron-irradiated Al

Application of a highly sensitive elastic-aftereffect technique, capable of resolving changes in strain as small as ±{} 5 ×{} 10^-9, has revealed the existence of an anelastic relaxation process due to the simultaneous migration and reorientation of single interstitials in recovery stage I of low-temperature electron-irradiated Al. Only the $〈100〉$-split interstitial configuration is consistent with the measured orientational dependence of the relaxation strength in single-crystal samples. The observed anisotropy of the interstitial dipole tensor is small, |P₁₁-P₂₂|=1.1±0.3 eV, showing that the long-range displacement field of this defect has nearly cubic symmetry. A comparison of the annealing of the relaxation strength with that of the resistivity shows a transition from correlated to uncorrelated recovery in stage ID+E. The thermodynamic properties characterizing the single-interstitial relaxation process explain why it has not been observed in previous internal-friction studies.