Dynamic crowdions, interstitials and vacancies in copper

Abstract

Abstract We determined the increase of the electrical resistivity in copper, Be doped copper, and in gold during irradiation with 1.85 MeV electrons below the temperature corresponding to the stage III recovery region. From the analysis of these data by means of rate equations we are able to determine the variations of the concentrations of interstitials, vacancies and agglomerates of interstitials as a function of the irradiation time and of the irradiation temperature. The number of replacement collision sequences of dynamic crowdions is about N = 4.104 before they convert into stable interstitials in well annealed pure copper, in commercial copper, and in pure gold. This number decreases with beryllium additions and is about N = 15 in copper doped with 763 ppm beryllium. The rate of spontaneous annihilation of vacancies with dynamic crowdions during irradiation depends on the number of replacement collisions sequences. Thus the production rate of vacancies and interstitials decreases in pure materials with increasing irradiation time considerably. However, the production rate of dynamic crowdions does not decrease with increasing irradiation time, i.e. with increasing concentrations of vacancies and interstitials and is equal to the initial production rate of interstitials. The initial production rate of point defects is the production rate determined for zero defect concentrations. The recovery of the stages III and IV were investigated for copper containing 763 ppm beryllium. After small irradiation doses mainly recovery stage III and after high irradiation doses mainly recovery stage IV is observed. For these two recovery stages activation energies of (0.72 ± 0.05) eV and (1.07 ± 0.05) eV are determined and attributed to the migration activation energies of interstitials and vacancies, respectively. These values are only very slightly larger than the ones determined for pure copper. Thus the migration activation energy of copper and beryllium in the dumbbell configuration is very similar to that of self-interstitials in pure copper and the binding energy of beryllium to vacancies must be very small.