The effective formation energies of vacancies and antistructure atoms on both sub-lattices were calculated, for an ideal model for the thermodynamically stable homogeneous ordered B2-compound, using a combination of ab initio electron theory and statistical mechanics. The results were compared with data for FeAl and NiAl, obtained using the same procedure, and with experimental results. The structural defects in CoxAl1-x were Co antistructure atoms, for x-values above 0.5, and Co vacancies, for x-values below 0.5; but the latter defects were only slightly more favourable than were Al antistructure atoms. This near-balance was thought to be perhaps responsible for the conflicting experimental results which were obtained using real Al-rich samples.

Atomic Defects in the Ordered Compound B2-CoAl - a Combination of ab initio Electron Theory and Statistical Mechanics. G.Bester, B.Meyer, M.Fähnle: Physical Review B, 1999, 60[21], 14492-5