Theory of self-diffusion in alkali metals: II. The influence of divacancies in Li

The formation energies and the binding energies of divacancies in bcc Li are calculated using the ab initio electron theory in a supercell approach. The results show that the activation energy for self-diffusion via divacancies should be much larger than that for self-diffusion via monovacancies. This is in contrast to the case for an analysis of the experimental self-diffusion data from the nuclear magnetic resonance relaxation rates in terms of a combined monovacancy-divacancy mechanism which would yield similar activation energies for monovacancies and divacancies. It is therefore concluded that a contribution from divacancies cannot explain the observed curvature of the Arrhenius plot for the self-diffusion data for Li at high temperatures.