The nucleation of dislocation loops from vacancies

Abstract

The nucleation of various aggregates of vacancies is considered. It is concluded that there is not sufficient supersaturation of vacancies during crystal growth from the melt to nucleate dislocation loops, partial dislocation loops, or vacancy discs. The stability of various configurations of vacancies at a moving interface is examined. The spontaneously occurring configurations are found to be unstable at normal growth rates. The formation of dislocations from the solid-like embryos that exist in the liquid is found to be an improbable process. None of the various mechanisms which have been suggested for the formation of dislocations from vacancies will account for the dislocations found in melt-grown crystals. In agreement with experiment, the theory indicates that there will be sufficient supersaturation of vacancies in samples which have been quenched from near the melting point to nucleate dislocation loops.