line Defects 1. edge defects 2. Screw defects

1. Presentation on:
CrystalDefects
Line Defects
1. Edge defects
2. Screw defects

2. Made by- Mehak Tariq
Roll No. Phys-M-18-17
Department of Physics
Ghazi University DG Khan
MehakTariq
Presentedby:

3. Crystal Defects
Definition : Imperfection in the regular geometrical arrangement
of the atoms in a crystalline solid. These imperfections result
from deformation of the solid, rapid cooling from high
temperature, or high-energy radiation (X-rays , Gamma rays)
striking the solid.
Gamma rays are
extremely high
energy waves
produced by nuclear
reactions.
Disordered atomic region is called
defect or imperfection.

4. Any irregularity in the pattern of crystal arrangement in a solid lattice is
called imperfection in solids.
The occurrence of defects takes place when crystallization (the process of
formation of crystals) occurs at a very fast or at an intermediate rate.
This is because particles don’t get enough time to arrange themselves in a
regular pattern.

8. Types of crystal defects
1. Point defects (0-D)
2. Line defects (1-D)
3. Surface defects (2-D)
4. Volume defects (3-D)

9. Line Defects
Line defects is also called dislocations.
Dislocations are areas were the atoms are out of position
in the crystal structure. Dislocations are generated and
move when a stress is applied.
Stress is internal
forces acting on the
object. The internal
forces are the result of
how forces are
applied to an object.
Irregularities or deviations from ideal arrangement in
entire row of lattice point is know as line defects.

10. ➢ Line defects or Dislocations are abrupt change in atomic order along a line.
➢ They occur if an incomplete plane inserted between perfect planes of atoms
or when vacancies are aligned in a line.
➢ A dislocation is the defect responsible for the phenomenon of slip, by which
most metals deform plastically.
➢ Dislocation form during plastic deformation, solidification or due to thermal
stresses arising from rapid cooling.

11. A dislocation is characterized by Burger’s vector, b.
It represents the magnitude and direction of distortion associated with
that particular dislocation.
Two limiting cases of dislocations, edge and screw, are characterized
by Burger’s vector perpendicular to the dislocation line (t) and
Burger’s vector parallel to the dislocation line respectively.
Burger’s vector for a dislocation line is invariant i.e. it will have same
magnitude and direction all along the dislocation line.
Line defects – Burger’s vector

12. Types of line defects or dislocations
1. Edge dislocation
2. Screw dislocation

13. Edge dislocations
An edge dislocation is defect when extra-
half planes of atom is introduced midway
through crystal.
It distort nearby planes of atoms,
When enough force is applied from one
side of crystal structure.
The extra-half plane will break its existing
bonds and form new bonds with its
neighbor opposite of the dislocation
motion.

14. Edge Dislocations
The animation show force is applied on upper
and lower surfaces.
Consequently an extra half-plane is
introduced.
Due to this extra-half plane the crystal is
badly distort.
This step is repeated in many discreet steps
until the dislocation has moved the entirely
through the lattice.
After all deformation ,the extra-half plane
forms is one unit step wide.

15. Edge dislocations

17. Screw dislocations
Screw dislocations is another type of line defect in which
the defect occurs when the planes of atoms in the crystal
lattice trace a helical path around the dislocation line.
When velocity vector is
not normal to the magnetic
field then the charged
particle follows a helix
path but not actually a
definite circular path.

21. Screw dislocations

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