Vacancies and self-interstitials in cadmium

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Abstract
The temperature dependence of tracer self-diffusion measurements in cadmium is analyzed in conjunction with investigations of the equilibrium concentration of vacancies by thermal expansion and positron annihilation. The following values for the monovacancy migration enthalpies are obtained: H M IV,A = 0.48 eV for A -jumps (nearest-neighbour jumps in the basal plane), H M IV,B = 0.40 eV for B-jumps (nearest-neighbour jumps out of the basal plane). A nomenclature for the recovery stages of irradiated cadmium is proposed that is fully analogous to that for f.c.c. metals. It is shown that Stage IV, for which an activation energy of (0.38 ± 0.03) eV has been measured, must be attributed to monovacancy migration, whereas Stage III, with activation energies varying between (0.23 ± 0.02) eV and (0.27 ± 0.03) eV, has to be assigned to the migration of self-interstitials. The spread in Stage-III activation energies and the unusual recovery kinetics may be understood in terms of a strong anisotropy in the diffusion coefficient of the self-interstitials. From this the configuration, the migration mode, and the activation energy of the Stage-III interstitial have been deduced.

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