Crystal defects impact the properties of crystalline materials. Point defects are irregularities around a single atom, such as vacancies where an atom is missing or interstitials where an extra atom is present. Line defects include dislocations where the ordered atomic planes are disturbed along a line. Surface defects occur at boundaries between regions with different crystal structures. Bulk defects are larger precipitates, inclusions, or voids within the material volume. Defects are classified based on their dimensionality and can be intentionally introduced to modify material properties.

1. CRYSTAL DEFECTS

2. INTRODUCTION
• Crystalline material has a crystal structure in
which the atoms are positioned in perfect
ordered pattern which is repetitive over large
atomic distance.
• Defects have a profound impact on the
macroscopic properties of materials.
• Sometimes defects are deliberately created to
improve properties of crystal.

3. 0D
(Point defects)
CLASSIFICATION OF DEFECTS BASED ON DIMENSIONALITY
1D
(Line defects)
2D
(Surface / Interface)
3D
(Volume defects)
Vacancy
Interstitial
Frenkel
defect
Schottky
defect
Edge
Dislocation
Grain
boundary
Twin
boundary
Dispersant
Precipitate
Inclusion
Voids /
CracksStacking
faults
Screw
Dislocation

4. POINT DEFECTS
Point Defects are the irregularities or deviations
from ideal arrangement around a point or an
atom in a crystallinesubstance.
0D
(Point defects)
Vacancy
Interstitial
Frenkel defect
Schottky defect
Non-ionic
crystals
Ionic
crystals

5. VACANCY DEFECT
 Atom missing from an atomic site
 Occur due to imperfect packing during crystallisation
 This results in decrease in density of the substance
 Number of vacancy defects depend on temperature
Missing atom

6. INTERSTITIALS DEFECT
 Addition of an extra atom within a crystal structure
 This defect increases the density of the substance
 Causes atomic distortion
 Vacancy and interstitials are inverse phenomena
Interstitial atom

7. SCHOTTKYDEFECT
 Pair of anion and cation vacancies
 In order to maintain electrical neutrality, the number of missing
cations and anions are equal
 It also decreases the density of crystal
 E.g. Alkali halides such as NaCl, KF, etc.

8. FRENKELDEFECTS
 Cation (being smaller get displaced to interstitial voids
 Combination of vacancy and interstitial atom
 No change in the density
 E.g. AgI, CaF2

9. LINE DEFECTS
• Line defects are the irregularities or deviations from
ideal arrangement in entire rows oflattice points.
• Interatomic bonds significantly distortedin
immediate vicinity of dislocationline.
• Dislocation affects the mechanicalproperties.

10. EDGE DISLOCATION
• POSITIVE DISLOCATION
• NEGATIVE DISLOCATION
SCREWDISLOCATION
The lattice/atomic planes
follow helical or spiral
along the dislocationline.

11. SURFACE DEFECTS
• Surface defects are associated withboundaries
that are separate regions of the materials and
have different crystalstructure.
• Two Dimensional defect.
• Due to change in orientation of the atomic
planes and stacking sequence of atomic planes.
• Caused during solidification or mechanicalor
thermal treatment ofmaterial.
• Effect the mechanical properties,electrical
resistance and corrosionresistance.

12. Bulk or Volume Defects
 PERCIPITATES : Fraction of a micron in size
 DISPERSANTS : may be large precipitates, grains, or polygranular
particles distributed through microstructure
 INCLUSIONS : foreign particles or large precipitate particles ;
undesirable ; harmful
 VOIDS : Trapped Gases ; Decreases mechanicalstrength
Cluster of microcracks in a
melanin granule irradiated
by a short laser pulse.

13. THANK YOU
J.KAUSHIK
180031369
S-12