Screened Interaction Model for Impurity Diffusion in Zinc

The screening theory proposed by Lazarus has been used to examine the impurity diffusion in zinc. The difference in the activation energies ($\Delta Q$) for the impurity diffusion and self-diffusion in zinc have been calculated using a screened Coulomb interaction between the vacancy and the excess charge $\mathrm{Ze}$ of the impurity ion. The change in the energy of formation of a vacancy next to the impurity ion is calculated by considering the electrostatic interaction between the impurity ion and the vacancy when they are nearest neighbors. In a saddle-point configuration, the diffusion ion may be assumed to be flanked by two half-vacancies. The change in the energy of motion has been calculated by considering the electrostatic interaction between the two half-vacancies and the impurity ion in the saddle-point configuration. Correlation corrections have been calculated using the expressions for the correlation factors. The estimated differences in activation energies for trivalent and monovalent impurities in zinc have been compared with the available experimental data. The estimated values check fairly well in the case of indium and gold, whereas the agreement is poor in the case of silver. Correlation corrections are important for a trivalent impurity, whereas the diffusional jumps of the monovalent impurity are relatively uncorrelated.