The energetics of Ni vacancy jumps in the intermetallic compound NiAl were studied by combining embedded-atom and first-principles calculations. The embedded-atom potential used here was fitted to both experimental and first-principles data and provided an accurate description of point defect energies and vacancy jump barriers in NiAl. Some of the embedded-atom results reported here, were independently verified by plane-wave pseudopotential calculations. The results suggested that the atomic configuration produced by a nearest-neighbor jump of a Ni vacancy was mechanically unstable. Because of this instability, the vacancy implements 2 sequential nearest-neighbor jumps as one collective 2-atom transition. Such collective jumps initiate and complete 6-jump vacancy cycles of a Ni vacancy, which were shown to occur by either 4 or 3 vacancy jumps. Next-nearest-neighbor vacancy jumps were shown to have diffusion rates comparable to experimental ones at the stoichiometric composition, suggesting that this was an important diffusion mechanism in NiAl.

Evaluation of Diffusion Mechanisms in NiAl by Embedded-Atom and First-Principles Calculations. Y.Mishin, A.Y.Lozovoi, A.Alavi: Physical Review B, 2003, 67[1], 014201 (9pp)