Space charge distributions near interfaces during kinetic processes

Abstract

For a variety of kinetic processes or transient conditions, such as grain boundary migration, formation of new surfaces at low temperatures, and quenching, there is insufficient time for solute redistribution around the interface. Under these conditions vacancy migration may be rapid. We analyze two limiting cases of constrained equilibria in which the vacancy distribution satisfies a minimum free energy under the constraint of no solute redistribution. The two cases are where the solute-vacancy association is at local equilibrium or is invariant. The resulting space charge potentials around the interface are often similar to that for the fully equilibrated case, if the bulk potential is controlled by vacancy equilibration. The differences in the electrostatic potentials among the constrained and complete equilibrium cases increase with decreasing temperature. The differences can also be increased if there are appreciable non-Coulombic solute-boundary interactions. Furthermore, we analyze the times, temperatures, or kinetic conditions under which these approximations are useful.