Question

Describe the difference between a point defect and a line defect and the effects on the crystal structure. Give an example and sketch of each of the two types.

Answer 1

Point Defects: Point defects are where an atom is missing or is in an irregular place in the lattice
structure. Point defects include self interstitial atoms, interstitial impurity atoms, substitutional
atoms and vacancies.

Line Imperfections:
In linear defects groups of atoms are in irregular positions. Linear defects are commonly called
dislocations. Any deviation from perfectly periodic arrangement of atoms along a line is called the
line imperfection. In this case, the distortion is centered only along a line and therefore the
imperfection can be considered as the boundary between two regions of a surface which are perfect
themselves but are out of register with each other. The line imperfection acting as boundary
between the slipped and un-slipped region, lies in the slip plane and is called a dislocation.
Dislocations are generated and move when a stress is applied. The strength and ductility of metals
are controlled by dislocations.

point defect example:

line defect example