  In this work we have studied the defect structure and corresponding defect
concentration investigations through the theoretical, experimental and
computational works on B2-type Fe-Al alloys. We have used ab initio framework
in order to investigate the defect structure. To have a proper explanation for
high defect concentration in B2-FeAl, we did not confine with point defect, but
extend the work on defect complexes. The possible defect formation energies
were calculated with the dependence of chemical potential and carefully
investigated against supercell size and the effect of magnetism. The
calculations revealed that the double Fe antisite at Fe rich condition, the
single Fe vacancy at intermediate region (i.e in the stoichiometry) and the
double Al antisite is the dominant defect close to Al rich condition, where
mainly Al rich region was unstable. From the obtained defect formation
energies, defect concentrations were calculated at different temperatures with
respect to Al concentration for B2-FeAl. It has been found that increasing Al
content and temperature gradually leads to increase in the vacancy content. It
has also seen that the dominant defect for all temperature ranges was the
single Fe vacancy at the exact stoichiometry and the highest single Fe vacancy
content detected with 1.6 % at 1450 K.
