A mean-field-type model was established to describe the concentration of point defects in binary NiAl by taking into account the effects of crystal expansion and off-stoichiometry. Different from some recent studies. This analysis showed that constitutional vacancies were present only in Al-rich NiAl at 0K but that the vacancy concentration decreased with increasing temperature until diffusion was activated and thereafter became almost independent of temperature. Such vacancy formation behavior in Al-rich NiAl belonged to the category of metastable constitutional type according to a method of classifying vacancy formation in B2 crystals.

Concentration of Point Defects in Binary NiAl. Y.L.Hao, Y.Song, R.Yang, Y.Y.Cui, D.Li, M.Niinomi: Philosophical Magazine Letters, 2003, 83[6], 375-84