DIFFUSION MECHANISM IN ORDERED ALLOYS - A DETAILED ANALYSIS OF 6-JUMP VACANCY CYCLE IN A TWO-DIMENSIONAL ORDERED LATTICE

Atom movements via six-jump vacancy cycle are analysed in detail for a two-dimensional ordered alloy, AB. The diffusion coefficients, D//A and D//B, are expressible in terms of the effective jump frequency, nu , for the six-jump vacancy cycle, and the correlation factors, f//A and f//B. By applying the theory of stochastic processes, the analytical expression for nu is derived in terms of six individual jump frequencies of vacancy. The correlation factors, f//A and f//B, can be calculated exactly: f//A equals 1/( pi minus 1), f//B equals pi /( pi plus 2).