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Evaluation of diffusion mechanisms in NiAl by embedded-atom and first-principles calculations School of Computational Sciences, George Mason University, Fairfax, Virginia 22030
 

Summary: Evaluation of diffusion mechanisms in NiAl by embedded-atom and first-principles calculations
Y. Mishin
School of Computational Sciences, George Mason University, Fairfax, Virginia 22030
A. Y. Lozovoi
Atomistic Simulation Group, School of Mathematics and Physics, The Queen's University of Belfast, Belfast BT7 1NN,
Northern Ireland, United Kingdom
A. Alavi
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
Received 6 July 2002; published 16 January 2003
The energetics of Ni vacancy jumps in the intermetallic compound NiAl are studied by combining
embedded-atom and first-principles calculations. The embedded-atom potential used in this work is fit to both
experimental and first-principles data and provides an accurate description of point defect energies and vacancy
jump barriers in NiAl. Some of the embedded-atom results reported here, are independently verified by
plane-wave pseudopotential calculations. The results suggest that the atomic configuration produced by a
nearest-neighbor jump of a Ni vacancy is mechanically unstable. Because of this instability, the vacancy
implements two sequential nearest-neighbor jumps as one collective, two-atom transition. Such collective
jumps initiate and complete six-jump vacancy cycles of a Ni vacancy, which are shown to occur by either four
or three vacancy jumps. Next-nearest-neighbor vacancy jumps are shown to have diffusion rates comparable to
experimental ones at the stoichiometric composition, suggesting that this is an important diffusion mechanism
in NiAl.

  

Source: Alavi, Ali - Department of Chemistry, University of Cambridge
Mishin, Yuri - Laboratory for Computer Design of Materials & School of Computational Sciences, George Mason University

 

Collections: Chemistry; Materials Science