CONCENTRATIONS OF ATOMIC DEFECTS IN B2-FEXAL1-X - AN AB-INITIO STUDY

The concentrations of various atomic defects are calculated within the framework of a grand canonical formalism for the ordered compound Fex Al1-x with B2 structure as functions of temperature and composition. T he input parameters for the grand canonical formalism are determined b y the ab-initio mixed-basis pseudopotential theory in local-density ap proximation. It is shown that FexAl1-x. is neither a compound with pur e antisite disorder nor a compound with pure triple-defect disorder bu t that it exhibits a hybrid behaviour in which vacancies on the Fe sub lattice and antisite atoms on both sublattices appear. The concentrati on of vacancies on the Al sublattice is negligibly small. The implicat ions of this result for the modelling of diffusion mechanisms in FexAl 1-x are discussed.