Lattice Vacancies in High-Purity α-Iron

The paper is both a review of the properties of vacancies in high-purity α-iron and an original contribution. In the review part it is shown that self-diffusion in α-iron occurs by the vacancy mechanism, that the sum of the monovacancy formation and migration enthalphies in the magnetically fully ordered state is HF1V + HM1V = (2.91 ± 0.04) eV, and that for the monovacancy formation enthalpy 1.61 eV ≤ HF1V ≤ 1.75 eV holds. The result for the monovacancy migration energy, HM1V = (1.23 ± 0.11) eV, excludes with certainty the attribution of Stage-III recovery to vacancy migration and supports the view that the Stage-III defect is a self-interstitial. It is shown that at elevated temperatures positrons trapped in vacancies in body-centred cubic iron may escape from them. The binding energy of positrons to the vacancies is estimated to be about 1.1 eV. This estimate is in agreement with the analysis of the high-temperature trapping of positive muon by vacancies, which in the present case proved to be the most sensitive technique for detecting vacancies present in thermal equilibrium.