A 6-frequency model was considered for the description of diffusion in binary A3B ordered alloys with the L12 structure. The model assumed that  a priori  sub-lattices existed. Three vacancy exchange frequencies described A-jumps from the  sub-lattice to the  sub-lattice and their reverse, plus intra- sub-lattice jumps. A further 3 exchange frequencies described B-jumps from the  sub-lattice to the  sub-lattice and their reverse, plus intra- sub-lattice jumps. Explicit expressions were derived for the average atomic jump frequencies for each atomic species. The thermodynamic factor for chemical diffusion was calculated by adapting the Widom formalism. Collective correlation factors were calculated by using the Manning relationships, and calculated tracer correlation factors for the present structure. These parameters were compared with computer simulation results, and good agreement was found. Analytical expressions were determined for the tracer and intrinsic diffusion coefficients. The formalism was used to place limits on the exchange frequencies in Ni3Al and Ni3Ge.

I.V.Belova, G.E.Murch: Journal of the Physics and Chemistry of Solids, 1997, 58[2], 311-8