Nonuniversal structure of point defects in face-centered cubic metals

Abstract

Using ab initio density function theory calculations, we have determined the structure of self-interstitial atom (SIA) defects in the most commonly occurring face-centered cubic (FCC) metals. The most stable SIA defects in Al, Ca, Ni, Cu, Pd, and Ag are the $\ensuremath{\langle}100\ensuremath{\rangle}$ dumbbells whereas octahedral SIA configurations have the lowest energy in Pt, Rh, and Th. The relative stability of defect configurations in Sr, Ir, Au, and Pb is less well defined, and calculations suggest that an SIA defect has the $\ensuremath{\langle}100\ensuremath{\rangle}$ dumbbell structure in Sr and Ir, a $\ensuremath{\langle}110\ensuremath{\rangle}$ crowdion/dumbbell structure in Au, and that it adopts an octahedral configuration in Pb. The occurrence of octahedral and $\ensuremath{\langle}110\ensuremath{\rangle}$ crowdion/dumbbell SIA configurations implies that defects diffuse one-dimensionally. This is fundamentally different from the three-dimensional translation-rotation migration characterizing the mobility of a $\ensuremath{\langle}100\ensuremath{\rangle}$ dumbbell. Elastic fields of point defects are defined by their elastic dipole tensors, which we compute for all the defect configurations. The magnetism of a $\ensuremath{\langle}100\ensuremath{\rangle}$ dumbbell in ferromagnetic nickel appears to have little effect on the structure of the defect. The variation of energy and elastic field of an SIA defect in copper is explored in detail as a function of its structural transformation along the migration pathway.