Question

Differentiate schottky and frenkel defects and discuss the effect on the density of crystals in both cases

Answer 1

Dear Student,

Schottky Defect	Frenkel Defect
Schottky defect occurs in those ionic crystals where difference in size between cation and anion is small.	Frenkel defect usually occurs in those ionic crystals where size of anion is quite large as compared to that of the cation.
In Schottky defect, both cation and anion leave the solid crystal.	In Frenkel defect, only the smaller ion (cation) leaves its original lattice site; whereas, the anion remains in original lattice sites.
The atoms permanently leave the crystal.	Here, atoms leave the original lattice site and occupy interstitial position. So atoms reside within the solid crystal.
One Schottky defect leads to the formation of two vacancies.	One Frenkel defect creates one vacancy and one self-interstitial defect.
Two atoms reduce from the crystal for each Schottky defect.	The number of atoms present in the crystal before and after Frenkel defect remains same.
Due to vacancy formation, Schottky defect reduces density of the solid.	Density of the solid crystal before and after Frenkel defect remains same as no atom leaves the solid.
Common materials where Schottky defect can be found are: Sodium Chloride (NaCl) Potassium Chloride (KCl) Potassium Bromide (KBr) Silver Bromide (AgBr) Cerium Dioxide (CeO2) Thorium Dioxide (ThO2)	Common materials where Frenkel defect can be found are: Zinc Sulfide (ZnS) Silver Chloride (AgCl) Silver Bromide (AgBr)

Due to vacancy formation, Schottky defect reduces density of the solid.
Density of the solid crystal before and after Frenkel defect remains same as no atom leaves the solid.

Regards

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