Calculations of the average driving force for electromigration in liquid-metal alloys

The average driving force for electromigration acting on ions of each species is calculated for a number of liquid alloys, using a pseudopotential approach due in its present form to Faber. According to the approach, the force acting on an ion is related, within the first Born approximation, to the contribution suitably defined of the ion to the alloy resistivity. The theory generally reproduces the experimental trends. In the case of NaₓK_1-x, for which calculations are carried out over the whole range of alloy concentration, the experimentally observed reversal in electromigration direction can be reproduced only at a cost of some loss in accuracy in the resistivity calculation. The numerical results indicate a correlation between effective valence and the effective hard-sphere diameter of an ion: in general, the smaller the solute ion, the more likely it is to migrate towards the anode.