Defect Structure and Thermodynamic Properties of the Wustite Phase (Fe 1‐ y O)

The defect structure model in the wustite phase is considered involving the 4:l cluster as a basic defect structure unit. Interactions between defects are considered in terms of the Debye‐Hückel theory for strong electrolytes. It has been shown that the available data on wustite nonstoichiometry fit well the 4:l cluster model. Above 1173 K the degree of ionization of the cluster is −5. The equilibrium constant of the cluster formation determined in this work is K c = [(( V Fe ) 4 Fe i ) 5− ][h] 5 [Fe Fe ] −6 [V i ] −1 P O2 −3/2 f 6 ± = 1.07 × 10 −14 exp[396.7 (kJ)/ RT ]. The equilibrium constant is quite consistent with such thermodynamic parameters as partial molar enthalpy and entropy of oxygen in Fe 1‐ y O within the entire stability range of the wustite phase.