Quasi-chemical reactions in solids

The ealeulations for equilibrium states involving strueture elements will be carried out using the quasi-chemical method, with equilibrium between reactions creating or involving those strueture elements. 

Definition and characteristics of a quasi-chemicai reaction between structure eiements 

When a solid enters into a reaction, we accept that it is, in faet, the structure elements which react. Similarly, the produetion or elimination of a defect in a solid is the consequence of reaetions which, necessarily, involve those structure elements. All these reactions can be represented by a formulation, similar to the 

Such reactions have a certain number of characteristics  

As an example, we will examine the reaction between gaseous oxygen and bariiun oxide. This oxide has interstitial cations and contains free electrons and therefore an excess of cations. At equilibrixun, this overstoichiometry is greater or lesser depending on the oxygen pressure, which reigns over the solid. This is due to a reaction which it is tempting to write with the usual chemical symbols in the form  

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