Calculation of the Entropies of Lattice Defects

Abstract

The entropy of lattice defects are here considered in somewhat greater detail than previously. Calculations are out to estimate the intrinsic entropies associated with such lattice defects as interstitialcies and vacancies, and with the activated complexes of vacancy and ring diffusion. The present application is to fcc metals and a very simplified force model representing only the closed-shell, ion-core repulsions of copper has been used. The problem consists in evaluating the change of lattice vibrations with the introduction of each defect. The method is in a first approximation to consider vibrations localized around the defect as separate from elastic vibrations at appreciable distance from the defect. Only in the region far from the defect is the entropy contribution always positive. The surface condition of zero pressure introduces a term which reduces the effect of the "localized" vibrations. In general the intrinsic entropy is less positive for those configurations where there is crowding of the atoms than for those configurations where the atoms have greater free volume.