(Solid state)
Hi! Can someone explain the Schottky and Frenkel defects.
Answers
Answer:
{\huge{\underline{\underline{\text{ \bf{Schottky Defects}}}}}}
Schottky Defects
● DEFINITION -
✮ In the ionic Crystal's, the defect forms when oppositely charged ions leave their lattice sites creating vacancies. The vacancies are formed in stiochimetric units, to maintain an overall neutral charge in the ionic solid.
✮ it is a type of point defect in crystal lattice named after Walter H. Schottky.
✮ In non - ionic crystals is it means and lattice with vacancies defect.
✮ If in an ionic crystals of the type \sf{A^{+}}A
+
\sf{B^{-}}B
−
equal number of cations and anions are missing from their lattice. It is also called Schottky defect.
✮ Just because the equal number of anion and cation are missing, the whole crystal are arrangement is maintained as electrically neutral.
✮ This occurs only when there is small difference in size of cations and anions.
✮ This type of defect is shown by highly ionic compounds such as NaCl , KCL , CsCl etc.
✮ And it also has coordination numbers
Important points to remember :-
❂ Equal number of Cations and Anions were missing from the lattice sites.
❂ Found in highly ionic compounds only with high coordination number and where Cations and Anions are of similar size.
❂ Density of the solid decreases.
{\huge{\underline{\underline{\text{ \bf{Frenkel Defects}}}}}}
Frenkel Defects
● DEFINITION -
✮ The Frenkel Defects is a type of Defeats in Crystalline Solids where in an atom is displaced from its lattice position to the interstitial site and an interstitial defects at the new location within the same element without changes in Chemical Properties.
It was named after the Soviet Physicist Yakov Frenkel who discovered it in 1926.
● This is Ionic Compounds which have :-
Low Coordination numbers.
Larger difference in size of Cations and Anions.
Compounds having highly polarising Cation and easily Polarisable Anion .
A few examples of ionic compounds exhibiting this defects are AgCl , AgBr , ZnS etc.
Important Points to remember :-
❂ A Cations leaves the normal lattice site and occupies the interstitial sites.
❂ Found in ionic compounds with low coordination numbers and where the Anions are much larger in size than cations.
❂ Density of the solid remains same.
Answer:
Schottky defect:
Same number of positive and negative ions are missing from their respective positions leaving behind a pair of holes. This defect is more common in ionic compounds with high coordination number with approximately equal size of cation and anion. The density of crystal decreases. This defect is observed in NaCl,CsCl,KCl,KBr etc.
Frenkel defect:
An ion leaves its correct lattice site and occupies an interstitial site. It is common in ionic compounds with low coordination number and large difference in size of cation and anion. This defect is observed in ZnS,AgCl,AgBr,AgI etc.
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