Feature article: Vacancies and self-interstitials in zinc and cadmium

The aim of this paper is to derive from experimental data reliable information on vacancies and self-interstitials in the hexagonal metals Zn and Cd, in particular on their migration enthalpies, and thus to put on a firm footing the interpretation of further experiments, e.g. in the fields of radiation damage and positron annihilation. The anisotropy of the migration process is fully taken into account. This allows us to identify unambiguously the stable self-interstitial configuration. In both Zn and Cd it is found to be the so-called c-dumb-bell, which is capable of ‘preferentially one-dimensional migration’ [migration enthalpies parallel to the hexagonal axis (0·35 ± 0·02)eV (Zn) and (0·23 ± 0·02)eV (Cd), perpendicular to the hexagonal axis (0·43 ± 0·06)eV (Zn) and (0·35 ± 0·05)eV (Cd)]. The dependences of the tracer self-diffusivities on temperature, pressure and (in the case of Zn) tracer mass are analysed and lead, together with differential thermal expansion studies of the vacancies in thermal equilibrium, to the following monovacancy migration enthalpies: jumps within the basal plane (0·50 ± 0·06)eV (Zn) and (0·47 ± 0·03)eV (Cd); jumps out of the basal plane (0·43 ± 0·06)eV (Zn) and (0·39 ± 0·03)eV (Cd). These values are in excellent agreement with those derived from quenching and irradiation experiments, which involve vacancy supersaturations.