Tracer diffusion by a divacancy mechanism in b.c.c. lattices

Abstract

Recent calculations of the energetics of divacancy formation and migration in sodium indicate that the most stable divacancy configuration consists of two vacancies at second nearest neighbour sites (2n divacancy) and that the most probable migration steps are exchange jumps between 2n and 1n divacancies and between 2n and 4n divacancies. This complicated migration mechanism involves three different divacancy configurations and two different saddlepoints. In this paper the results of a calculation of the diffusion coefficient, correlation factor and isotope effect for a divacancy mechanism of self diffusion are reported and briefly discussed. Since the divacancy migration involves more than one saddlepoint the correlation factor and the isotope effect are in general temperature dependent.