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Abstract
In A3B alloys with the D03 structure, A atoms have nearest-neighbour A atoms, while B atoms are surrounded by unlike A atoms. Therefore the A atoms can diffuse by exchanging sites with vacancies on their own sublattices without concomitant disordering. The lattice formed of A atom sites only, namely the defective (DD) lattice D03, is a new type of lattice with cubic symmetry containing two different types of site with coordination numbers four and eight. The random-walk properties of the DD lattice are found to be intimately related to those of the f.c.c. lattice. The correlation factor f for self-diffusion is calculated rigorously: f = 0·605 292.
The isotope-effect coefficient E is derived from a simple model of impurity diffusion. Although there are two types of jump in the DD lattice, it is shown that they have the same ΔK kinetic factor and that the usual E = fΔK relation is valid.