Comprehensive ab initio thermodynamic treatment of impurities in ordered alloys: application to boron in B2 Fe-Al

A rigorous description of impurities in nearly stoichiometric ordered systems, relying on independent-point-defect thermodynamics and density-functional-theory ab initio calculations, is presented and applied to the study of the equilibrium point defect structure of Fe-Al-B alloys in the B2 composition domain (x(Al) approximately 50 at. %, x(B) approximately 0), including the influences of (i) magnetism and (ii) the local density approximation (LDA) or generalized gradient approximation (GGA) exchange-correlation functionals. Whatever the alloy composition, B substitutes for Al, except in the nonmagnetic GGA scheme predicting a switch towards interstitial occupancy for sufficient Al contents.