Calculations of the driving force of electromigration in hcp metals: Zn, Cd, Mg

Using a pseudopotential, weak-scattering formalism we calculate the driving force for electromigration by the vacancy mechanism in the hcp metals Zn, Cd, and Mg. The general formula is evaluated in a succession of approximate models to illustrate the influence of different physical effects. The final results are compared both with the experimental data and with a previous evaluation for Zn. Our form factors, which have been fit to low-temperature data and then scaled to account for volume changes near the melting point, yield an effective valence for the wind force of about twice the experimental value and only in qualitative agreement with the observed anisotropy. Possible resolutions are discussed.