By using the mean-field first-nearest neighbour interaction approximation, a unified model was derived for point-defect formation in such compounds. This accounted for defect structures which included the triple-defect type, antistructure defect type and hybrid type. The mathematically simple model clearly revealed the physical processes which governed point-defect production and defect type in intermetallics. Thus, competition between antistructure defect formation and vacancy formation determined the type of intermetallic and defect concentration. The model yielded excellent quantitative agreement with experimental results on the compositional and temperature dependences of the vacancy concentrations for 3 different types of intermetallic. On the basis of recent experimental results, and present model, it was concluded that no constitutional vacancies existed in any such intermetallic; including NiAl. Moreover, the abnormally high vacancy concentrations in such triple-defect compounds could be easily understood in terms of a competition between antistructure defects and vacancies. The energy barrier between the forming vacancy configuration and the antistructure defect configuration distinguished 3 apparently different types of B2 intermetallic, and there existed no fundamental difference between 3 apparently different types of intermetallic. It was predicted that the vacancy concentration was asymmetrical with respect to stoichiometry for all B2 intermetallics; including the antistructure-defect type. The vacancy concentration at high temperatures could be quite substantial (0.5 to 1%); even in antistructure-defect type B2 intermetallics, which were believed to contain only a negligible number of vacancies. The principles of point-defect formation which were established here for B2 intermetallics were suggested to apply to intermetallics having other structures.

A Unified Model for Point-Defect Formation in B2 Intermetallic Compounds. X.Ren, K.Otsuka: Philosophical Magazine A, 2000, 80[2], 467-91