Correlations in the arrangement of antistructure point defects in intermetallic phases with B2 (CsCl) structure

Abstract Based on the Bragg-Williams approximation, a statistical-thermodynamic approach is presented for non-stoichiometric binary B2 phases with a pure anti-structure defect mechanism. Whereas in the original Bragg-Williams model only the state of long-range order is considered and no correlations are allowed in the arrangement of the point defects, short-range order is introduced as an equilibrium property of the system in the present work. This new approach is applicable not only both to highly ordered intermetallic compounds and to completely disordered alloys but also in the region of the order-disorder transition. The obtained phase boundary which describes the order-disorder transition is in good agreement with the results predicted by Monte Carlo calculations.