What Dictates the Dominance of Frenkel vs Schottky Defects?

AI Thread Summary
The discussion focuses on the factors determining the dominance of Frenkel versus Schottky defects in crystal structures. Frenkel defects involve cation displacement to interstitial positions, while Schottky defects involve the displacement of both a cation and an anion. The proximity of ionic masses and their radii significantly influence which defect is more prevalent; similar mass and size between cations and anions tend to favor Schottky defects. Additionally, when the vacancy energies of anions and cations are comparable, Schottky defects are more likely to occur. Overall, the interplay of ionic size and mass plays a crucial role in defect formation in crystals.
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A question for anyone that has the ability to answer:

I understand the difference between Frenkel and Schottky defects, and I also know that in different crystal structures, which one is predominant is different. I was wondering, what dictates which defect is the dominant one?

Thanks for any responses!
 
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Frenkel defect occurs when a cation is displaced into an interstitial position, whereas a Schottky defect occurs when an anion (- ion) and a cation are displaced.

I have an example in one book that shows Frenkel defect in AgCl and Schottky defect in NaCl.

Na (A=23) and Cl (A=35) are close in mass, where as Ag (A=108) is heavier. The closer in mass the cation and anion, it would seem that it is more likely both would be equally displaced from the proper lattice position. Also, ionic radius probably plays a role.

More generally, if the anion and cation vacancy energies are similar, then it would stand to reason that Schottky defects are more likely than Frenkel defects.

I don't know if this is any use, but - http://www.iop.org/EJ/article/0953-8984/11/22/102/cm11022l2.html (registration maybe required).
 
Yes, that makes sense. I suspected that the relative sizes of the ionic radii would have some bearing on it. Thanks!
 
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