Equilibrium Population of Frenkel Defects in a Crystal

The estimation of the number of Frenkel defects in a crystal can proceed along lines parallel to those for Schottky defects by estimating the configurational entropy (Supplementary Material S4). This approach confirms that Frenkel defects are thermodynamically stable intrinsic defects that cannot be removed by thermal treatment. Because of this, the defect population can be treated as a chemical equilibrium. For a crystal of composition MX, the appropriate chemical equilibrium for Frenkel defects on the cation sublattice is 

In the case where the number of normal and interstitial sites is the same, that is, 

The Gibbs energy, AGcf, is often replaced by the enthalpy of Frenkel defect formation, AHcP, as described above, to give 

A similar equation can be written for Frenkel defects on the anion positions  

TABLE 2.2 Formation Enthalpy of Frenkel Defects in Some Compounds of Formula MX and MX2 

---