The thermodynamic characterization of an isolated ternary compound having a fixed cationic content is extended to include the effects of association of multiply charged point defects. BaTiO3 containing a stoichiometric excess of TiO2 is again used as a specific example. Defect association can remove the commonality of defect types originating from different sources, e.g., from nonideal cation ratios and from changes in nonmetal activity.
As a result, the strong dependence of cation activities on the nonmetal activity can be greatly reduced in certain cases, and the possibility that changes in nonmetal activity will drive the compound into a two-phase region may be decreased accordingly.
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