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1. Defects In Crystalline
Materials.

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3. Defects In Crystalline Materials.
 Metals, many ceramics and some
polymers are crystalline.
 Real crystals contain various types of
imperfections.
 Many of the important properties of
materials are due to the presence of these
imperfections.

4. Types Of Defects.
 Defects are categorized as:
1) Point defects.
2) Surface defects.
3) Volume defects.
4) Line defects.

5. Point Defects.
 All the atoms in a perfect lattice are at
specific atomic site.
 In a pure metal two types of point defects
are possible.
1) Vacancies.
2) Interstitial point defects.

6. Vacancies.
 Vacant atomic sites in
a structure.
 Due to plastic
deformation & high
energy particle
irradiation.

7. Interstitial Point Defects.
 “Extra" atoms positioned between atomic
sites.
 Due to plastic deformation & high energy
particle irradiation Interstitial
atom
distortion
of planes

8. Extrinsic Point Defects.
 Introduction of outsider atom.
 They play an important role in physical &
mechanical properties.
 Impurity atom can take two different sites
in crystal.
 Substitutional or Interstitial.

9. Point Defects
vacancy Interstitial
impurity
Substitutional
impurity

10. In metallic solids defects are not so
important but in ionic solids presence of a
vacant site (e.g. in NaCl), changes the
electrical properties.

11. Schottky & Frenkel Defects
 In order to conserve the overall neutral
charge vacancy must be occurred either in
pairs of opposite sign forming die-
vacancies called Schottky defects.
 In association of the interstitial of same ion
called Frenkel defects.

12. Defects in ionic solids
Frenkel
defect
Cation vacancy
+
cation interstitial
Schottky
defect
Cation vacancy
+
anion vacancy

13. Stacking Faults.
 Stacking fault is a planner defect and formed
when regular sequence of stacking is disturbed.
 Stacking faults are not may observed In planes
where the stacking sequence is
ABABAB….because there is no alternative site
for “A” layer other than resting on a “B” layer of
vice versa.
 In ABCABABC….layers it is visible.

14. A
B
C

15. Types Of Stacking Faults.
1) Intrinsic stacking faults.
2) Extrinsic stacking faults.

16. Intrinsic Stacking Faults.
 Removal of a layer from an arranged
sequence layer.
 E.g. CBACBA…..becomes CBABAC….

17. Extrinsic Stacking Faults.
 Addition of layer to the arranged sequence
layer.
 E.g. BACBAC….becomes BACABAC…

18. Grain Boundaries.
 A Grain Boundary is a general planar
defect that separates regions of different
crystalline orientation (i.e. grains) within a
polycrystalline solid.
 The atoms in the grain boundary will not
be in perfect crystalline arrangement

19. Grain Boundaries Cont...
 Grain boundaries are
usually the result of
uneven growth when
the solid is
crystallizing.