The dislocation density in 6N-purity material was decreased, to between 105 and 107/m2, by cyclic annealing. In such material, there were only a few sources for vacancy generation, and it was expected to require a long time in order to attain a thermal equilibrium concentration of vacancies. The electrical resistance was measured accurately at high temperatures in order to monitor the generation rate of vacancies. It was found that it required several hours to attain thermal equilibrium. The generation profiles for pre-existing dislocations and interstitial-type dislocation loops were estimated by using a diffusion-limited model. It was concluded that, even in a high-quality crystal, most of the vacancies were generated by pre-existing dislocations, while only a small fraction was generated by the growth of interstitial-type dislocation loops. The surface oxidized at a rate of about one atomic layer per hour, and was not effective in generating vacancies.

Thermal Generation of Vacancies in High-Quality Aluminium Crystals H.Osono, E.Hashimoto, T.Kino: Philosophical Magazine A, 1998, 77[5], 1147-60