It was recalled that the antistructural bridge mechanism was a form of vacancy mechanism in binary ordered alloys and intermetallic compounds and was an important contributor to diffusion in the presence of substantial antistructural disorder. The limits on the antistructural bridge mechanism were established here for a number of jump possibilities of each component in an A3B alloy with the L12 structure. The general vacancy model which was used assumed that sub-lattices existed a priori. Three vacancy-exchange frequencies described A jumps from the a sub-lattice to the ß sub-lattice, and its reverse, plus intra-a sub-lattice jumps. Another 3 exchange frequencies described B atom jumps from the ß sub-lattice to the a sub-lattice, and its reverse, plus intra-a sub-lattice jumps. The limits of the antistructural bridge mechanism were determined analytically by using percolation arguments, and were checked via computer simulation. The A component did not exhibit percolation-threshold behavior within a useful range of compositions. The B component exhibited several types of percolation behavior, depending upon which jumps were operative. An especially interesting interstitialcy-like mechanism was identified in which the A atoms diffused by intra-a sub-lattice jumping which assisted B-atom diffusion via inter sub-lattice jumps.

Percolation and the Anti-Structural Bridge Mechanism for Diffusion in Ordered Alloys of the L12 Type. I.V.Belova, G.E.Murch: Intermetallics, 1998, 6[5], 403-11