Wiistite point defects

As in the case of wiistite, one of the earliest applications of atomistic simulations was to explore the likely stability of this defect cluster. It was found that not only the 2 2 2 arrangement but also other cluster geometries were preferred over isolated point defects. 

We saw in our discussion of phase diagrams that FeO never exists. Consider wiistite with composition Fco.gsO. To compensate the charge of Vpe (i.e., for electrical neutrality), we need to replace 3Fe " ions by 2Fe ions. This is the important point the Fe ions change their valence from 2 to 3. This point defect reaction happens automatically. You can imagine it occurring by dissolving Fe203(s) in FeO(s). 

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