What Dictates the Dominance of Frenkel vs Schottky Defects?

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SUMMARY

The discussion centers on the factors influencing the dominance of Frenkel versus Schottky defects in crystal structures. Frenkel defects occur when a cation is displaced into an interstitial position, while Schottky defects involve the displacement of both a cation and an anion. The predominance of these defects is dictated by the relative masses of the ions and their ionic radii. Specifically, when the cation and anion have similar vacancy energies, Schottky defects are more likely to occur, as illustrated by examples in AgCl and NaCl.

PREREQUISITES
  • Understanding of Frenkel and Schottky defects in crystallography
  • Knowledge of ionic radii and their significance in defect formation
  • Familiarity with vacancy energy concepts in solid-state physics
  • Basic principles of crystal structures and lattice positions
NEXT STEPS
  • Research the role of ionic radii in defect formation in various materials
  • Study the energy considerations of cation and anion vacancies in ionic compounds
  • Explore the implications of defect types on the physical properties of materials
  • Examine case studies of Frenkel and Schottky defects in different crystal structures
USEFUL FOR

Materials scientists, solid-state physicists, and students studying crystallography or defect structures in ionic compounds will benefit from this discussion.

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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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