Ab initiostatistical mechanics for alloy phase diagrams and ordering phenomena including the effect of vacancies

The effect of vacancies on the phase diagram and the order-disorder transition of a binary alloy is studied within the framework of an ab initio statistical mechanics. It is shown that for systems with structural vacancies the phase diagrams are substantially modified by the vacancies, both qualitatively (appearance of new vacancy-ordered phases) and quantitatively (stabilization of phases for a wider composition range, decrease of transition temperatures). The interplay of vacancies and antistructure atoms for the order-disorder transition is elucidated.