Defect clusters in wustite, Fe 1- xO

A quantum chemical approach based on predominantly covalent "normalized ion energies" has been developed for estimating structures and energies for defect clusters in quenched nonstoichiometric wustite (Fe _{1- x}O). Small defect clusters of zinc blende structure show special stability over other clusters considered. Of these, either a 13:5 or a 16:7 defect cluster (13 or 16 Fe ³⁺ vacancies and 5 or 7 tetrahedral Fe ³⁺ interstitials) have the proper structure and composition to account for the observed P' and P″ phases in wustite.