Question

Write types of defects and describe Schottky and Frenkel defects.Write answer of the given question in detail.

Answer 1

The defects in crystalline solids are of two types viz.,(1)Point defect (2) Line defect.
Point defect is further classified as :
(a)Vacancy defect or Scottky defect
(b)Interatitial defect or frenkel defect
(c) Impurity defect :
This is further classified as
(i)Substitution impurity defect.
(ii)Interstitial impurity defect.
(2)Line defects are further classified as
(a)Edge dislocation
(b) Screw dislocation
1) SCOTTKY DEFECT :-
1. In this defect , during crystallization , some of the lattice points remain unoccupied by the constituent particles.
2.In this case of ionic solids,the the vacancies are produced due to absence of cations and anions .Then these defects are called Scottky defects.
3. In this ionic solids , the expected density is less than the expected value.
4.These defects are observed in the solids with cations and anions of almost equal size.E.g. NaCl, KCl.
2)FRENKEL DEFECT:-
1.In this an ion in the ionic solid leaves a regular lattice site and occupies a place between the regular lattice points or interstitial points.This defect is called frenkel or interstitial defect.
2.Frenkel defect arises in case of ionic solids with relatively smaller cationic size which can fit into interstitial space and difference in ionic radii is large.This defect is called dislocation defect.
3.This defect is observed in AgCl solid by Ag+ ions ,in ZnS solid by ZnS2+ ions,etc.
4.frenkel defect does not alter the density of the crystalline solid.



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