This document discusses different types of defects in crystalline materials, including point defects, line defects, and interfacial defects. Point defects are localized atomic disorders, while line defects called dislocations are one-dimensional defects caused by misaligned atoms. There are three main types of dislocations: edge dislocations caused by extra half planes of atoms, screw dislocations from shear deformation, and mixed dislocations containing both. Interfacial defects include surfaces, grain boundaries between crystal regions, twin boundaries of mirrored lattices, and stacking faults interrupting the sequence of packed crystal planes.

1. Introduction of defects
• Based on the geometry crystalline imperfections are
classified:
Point defects, Line defects, Interfacial defects and bulk or
volume defects

2. Point defects in metals
• Point defects are of zero dimensional i.e. atomic disorder
is restricted to point-like regions.

3. • In ionic crystals, defects can form on the condition of charge
neutrality. Two possibilities are:
Point defects in ceramics

4. Line Defects
• Linear defects (Dislocations) are
one-dimensional defects that cause
misalignment of nearby atoms.
• Slip between crystal planes result
when dislocations move
• Dislocation movement produce
permanent (plastic) deformation.
• Types of dislocation
1. Edge Dislocation
2. Screw Dislocation
3. Mixed Dislocation
Schematic of Zinc (HCP):
before deformation
after tensile elongation
slip steps

5. Edge Dislocation
• Extra half-plane of atoms inserted in a crystal structure
• Around the dislocation there is some localised distortion
• Burger vector b is perpendicular to dislocation line
• Also called as Taylor-Orowan dislocation

6. Screw Dislocation
• Results from shear deformation
• Burger vector parallel to dislocation line
• Regions of shear stress around dislocation
line
• Also called as burger’s dislocation
• Mixed dislocation
• Contains both edge and screw dislocation
• Burger vector parallel to dislocation

7. Interfacial defects
• External Surfaces: Surface atoms are not bonded to the
maximum number of nearest neighbors, and are therefore in
a higher energy state than the atoms at interior positions
• Grain boundaries: Regions between crystals
transition from lattice of one region to another
Grain boundaries

8. • Twin boundaries: mirror-lattice symmetry
atoms on one side of the boundary are located in mirror-
image positions of the atoms on the other side
Twins formed due to shear forces(mechanical) and heat-
treatment(annealing)
• Stacking faults: interruption in stacking sequence of
closed packed planes:
Stacking fault in FCC : ABCABCABABCABAB
Stacking fault in HCP : ABABAABAABB