Special quasi-random structures were developed for substitutional random pseudo-binary A1−xBxC B2 alloys at compositions with x = 0.25 and 0.5. The structures mimicked the local pair and multi-site correlation functions of the corresponding random simple-cubic alloy. The quasi-random structures were used to study non-stoichiometric B2 NiAl alloys containing high concentrations of constitutional point defects. Direct first-principles calculations of the quasi-random structures provided the formation enthalpies, equilibrium lattice parameters and elastic constants of non-stoichiometric B2 NiAl alloys; in satisfactory agreement with published experimental data. The calculations unambiguously showed that Ni vacancies and Ni antisites were the stable constitutional point defects in Al-rich and Ni-rich B2 NiAl, respectively; up to large deviations from stoichiometry. Quasi-random structures calculations also confirmed the experimentally observed structural instability of B2 NiAl at high Ni concentrations. It was demonstrated that the quasi-random structures could even give the formation enthalpies of isolated defects; in good agreement with 54-atom super-cell calculations.

First-Principles Study of Constitutional Point Defects in B2 NiAl using Special Quasi-Random Structures. C.Jiang, L.Q.Chen, Z.K.Liu: Acta Materialia, 2005, 53[9], 2643-52