Self-diffusion and correlation effects in ordered AuZn alloys

Simultaneous self-diffusion measurements of Zn and Au in near-equiatomic highly ordered AuZn (B2 structure) single-crystal specimens having 49.0, 50.0, 51.0 at.% Zn nominal composition were made over a temperature range of 428-650°C using Zn65 and Au195 radioactive tracers and the serial lathe sectioning technique. Employing a modified energy-discrimination method for nuclear counting, it was possible to measure the ratio of diffusivities DZnDAu-in addition to their individual values-following simultaneous diffusion of the two radioactive tracers in the same specimen. The diffusion parameters Q and D0 and the entropy of activation factor were computed in the composition range studied and compared with the corresponding quantities in the disordered Zn-base monovalent alloys (A2 structure). The magnitude of the ratio of the correlation factors in ordered and disordered phases was found to be consistent with the correlated six-atom-vacancy-jump diffusion mechanism in the highly ordered alloys. The self-diffusion data for Au and Zn in -AuZn alloys also provides strong evidence for the presence of a nonequilibrium vacancy-defect structure on the Zn-rich side of stoichiometry. © 1971 The American Physical Society.