Calculations of the properties of self-interstitials and vacancies in the face-centred cubic metals Cu, Ag and Au

Abstract

The properties of self-interstitials and vacancies in the noble metals Cu, Ag and Au were calculated using interatomic potentials derived entirely from first principles. Self-interstitials were found to be stable in the (100) dumbbell (or split) configuration. Their formation and migration energies were 2.61, 2.20, 3.81 and 0.11, 0.07 and 0.11 eV for Cu, Ag and Au, respectively. On the other hand, the respective energies of vacancy formation and migration were calculated to be 1.42, 1.37, 2.75, and 0.82, 0.54 and 0.71 eV. Good agreement between the present theoretical predictions and experimental measurements was obtained for Cu and Ag. In the case of Au, only the calculated vacancy migration energy was in good accord with experiment; the other quantities showed various inconsistencies with regard to experimental observations. For example, the results for self-interstitials could not explain the abnormality of the post-irradiation recovery stage I and interstitial clustering at about 5K observed experimentally in Au. Furthermore, the energy of vacancy formation was three times larger than the measured value. These discrepancies are ascribed mainly to the less reliable nature of the Au potential, relative to those for Cu and Ag, which results from the decrease in the justification for the applicability of perturbation theory. Calculations of the defect properties in Al, another face-centred cubic metal, for which the first-principles interatomic potential has been available, are also included for the purpose of comparison.