The effects of association and dissociation processes on the anelastic behavior of solute-point defect complexes

Abstract

The standard discrete atomic jump model of the relaxation of point defect-solute pairs is augmented by a dynamic continuum model reflecting the effect of the surroundings of the complex. Effective-medium theory is used to derive the response characteristics of this continuum. In this way the effect of dissociation and association of solute-defect pairs on the anelastic behavior of a solid is described quantitatively. The model leads to the prediction of an additional very low-frequency internal friction peak when experiments are carried out at fixed temperature. The relaxation is identified with the ‘‘reaction mode’’ discussed earlier by Nowick. It is investigated in some detail for doped oxide materials. However, the emphasis here is directed less towards extensive comparison with experiment than towards an exposition of the new methodology. For this reason only nearest-neighbor binding between defect and solute is considered and only the trigonal pair in cubic materials is analyzed. However, the generalizations that are necessary in order to remove these restrictions are described.