Experimental data on diffusion, and the mechanisms of self-diffusion in the ordered structures were reviewed. It was noted that the B2-type structure was the most extensively experimentally and theoretically studied one with regard to diffusion behaviour. One such mechanism was the 6-jump vacancy cycle, which permitted diffusion to occur exclusively via nearest-neighbour vacancy jumps. The present author derived an analytical expression, for diffusion via the 6-jump vacancy cycle in the B2 lattice, in terms of the individual frequencies of vacancy jumps. The isotope effect in diffusion was considered quantitatively on the basis of the expression for the diffusion coefficient. This required self-diffusion coefficients for the constituent elements. In the case of L12 compounds such as Ni3Al, the self-diffusion coefficient for Al could be estimated from the interdiffusion coefficient and the tracer diffusion coefficient of Ni. The ratio, DAl/DNi, of the diffusion coefficients was equal to between 0.8 and 1.3. The ratio, DGa/DNi, was equal to 0.43 and the ratio, DGe/DNi, was equal to 0.007; all at an homologous temperature of 0.85.

Defects and Diffusion in Intermetallic Compounds. M.Koiwa: Radiation Effects and Defects in Solids, 1999, 148[1-4], 87-8