Self-correlation functions for impurity diffusion in hexagonal lattices

Abstract

Long-range diffusion of the substitutional impurity in the otherwise monoatomic hcp-like lattices (H1 type) via the monovacancy mechanism has been considered within the encounter approximation. A five-frequency model (valid for cubic lattices) extends here naturally into a sixteen-frequency model, leaving fourteen normalized frequencies, the latter describing an anisotropic part of the self-correlation function. Two simplified cases can be distinguished: a self-diffusion being described by a single normalized frequency and a true hcp lattice, where only three normalized frequencies remain independent of each other. A general formalism is discussed and a few examples are evaluated numerically.