Intrinsic Defects Trends and Further Considerations

Exchange of the interstitial Bi atom with an A atom on its correct site, Aa  

The interstitial Aj atom can eliminate the vacancy to form an A atom antisite defect  

If these three equations are added, the result is again 

These indirect mechanisms may be energetically preferable to a direct exchange of atoms. 

At all temperatures above 0°K Schottky, Frenkel, and antisite point defects are present in thermodynamic equilibrium, and it will not be possible to remove them by annealing or other thermal treatments. Unfortunately, it is not possible to predict, from knowledge of crystal structure alone, which defect type will be present in any crystal. However, it is possible to say that rather close-packed compounds, such as those with the NaCl structure, tend to contain Schottky defects. The important exceptions are the silver halides. More open structures, on the other hand, will be more receptive to the presence of Frenkel defects. Semiconductor crystals are more amenable to antisite defects. 

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