The Mechanism of Self-Diffusion in Alkali Metals

Abstract

On the basis of calculations of the activation energies of various ring, vacancy, and interstitial mechanisms in alkali metals, the most probable mechanism of self-diffusion is found to be the rapid transmission of short linear regions of compression (referred to as "crowdions") along body-diagonals in the body-centered cubic lattice. The creation of crowdions, which can be regarded as interstitial atoms diluted over a region of about eight interatomic distances in a vernier-like fashion, occurs at the surface rather than in the interior of a perfect lattice. The calculation of the corresponding energy of formation depends on the empirical values for the work function, heat of sublimation, and ionization energy; for sodium, the total heat of activation for diffusion by crowdions is probably less than one-tenth of one electron volt.