DIFFUSION BY ANTI-STRUCTURE DEFECTS IN NONSTOICHIOMETRIC INTERMETALLIC COMPOUNDS WITH B2 AND L1(2) STRUCTURES

Self-diffusion in non-stoichiometric intermetallic compounds with the B2 and Lit structures has been considered. It was shown that the therm al and compositional antistructure defects substantially affect the di ffusivity forming 'anti-structural bridges' for a vacancy migration wi thout additional disordering of the intermetallic compound. While this contribution was found to have a percolation nature for both sublatti ces in the case of the B2 structures, the percolation is to be taken i nto account only for diffusion of the minor element in AB(3) intermeta llic compounds with the L1(2) structure. The numerical calculations we re carried out for the CoGa triple-defect intermetallic compound. Crit ical exponents and fractal characteristics of percolation clusters wer e estimated. Values of the threshold anti-structure defect concentrati ons are 0.049 +/- 0.002 for B2 structures and 0.0347 +/- 0.0008 for th e alpha-sublattice of the AB(3) compound with the Lit structure. Owing to the temperature dependence of defect concentration the percolation threshold is temperature dependent also and, e.g., corresponds to Co5 2.4Ga47.6 composition at T = 1323 K. The theoretical predictions are c ompared with experimental data.