Defects in metal-deficient cobalt-wüstites, (Co, Fe)1−yO
Abstract By a simple statistical thermodynamic approach an equation describing the variation of nonstoichiometry with oxygen pressure is derived for metal-deficient oxides assuming that the predominant defect is of the type: 4V″ Fe , Fe … i . Comparing experimental data obtained by thermogravimetric equilibration measurements with data calculated from this equation shows good agreement both for pure Fe 1− y O (wustite) throughout the whole nonstoichiometry range and for (Co, Fe) 1− y O at low and moderate degree of nonstoichiometry. For the latter oxides, however, deviations are observed at high nonstoichiometry indicating that ordering probably takes place in this system at high defect concentrations.