Kinetics of Vacancy Motion in High-Purity Aluminum

Abstract

It is shown that in very high-purity aluminum, ${\mathrm{Al}}_{\mathrm{II}}$, the rate of vacancy annealing depends on vacancy concentration and annealing temperature but is independent of the temperature ${T}_{i}$ of vacancy injection per se. The rate can be described as the sum of first and second order components. The first order component becomes most prominent at a monovacancy concentration estimated to be ${10}^{\ensuremath{-}6}$ atom fraction. It is shown that the results are consistent with the Koehler-Seitz-Bauerle dissociative mechanism. The activation energy for diffusion of monovacancies in ${\mathrm{Al}}_{\mathrm{II}}$ is found to be 0.65\ifmmode\pm\else\textpm\fi{}0.06 ev. This, combined with earlier results on the formation energy of vacancies, gives 1.44\ifmmode\pm\else\textpm\fi{}0.11 ev for the activation energy for self-diffusion in aluminum by a monovacancy mechanism.In zone-refined aluminum, ${\mathrm{Al}}_{\mathrm{I}}$, of lesser purity the rate of vacancy annealing depends upon ${T}_{i}$ per se and falls off more rapidly with decreasing vacancy concentration than in ${\mathrm{Al}}_{\mathrm{II}}$. Two hypotheses for the impurity effects are considered, namely: (1) trapping of vacancies by impurity atoms and (2) inhibition of dislocation climb by adsorbed impurities.