Classify the Crystal Imperfections and explain Edge and screw dislocation.
edge and screw dislocation • 387  views

Crystal imperfections are classified as follows:

1) Point Defects(0D Imperfections)

i) Vacancy Defect

ii) Schottky defect

iii) Self-Interstitial defect

iv) Frenkel defect

2) Line Defects (1D Imperfections)

i) Edge dislocation

ii) Screw Dislocation

3) Surface Defects (2D Imperfection)

i) Grain boundaries

ii) Tilt boundaries

iii) Twin boundaries

iv) Stacking faults

4) Volume Defects (3D Imperfections)

i) Void

ii) Inclusions

Edge Dislocation

1) Whenever a layer of atoms is half inserted into the crystal lattice, the adjacent layers get shifted at the position of insertion and creates dislocation of other layers, such dislocation is known as edge dislocation.

2) The insertion of such layer of atoms create a stress concentration in that region, it also affects the density at that region.

3) It is measured by burger vector, and burger vector is in the plane of dislocation.

4) Due to such insertion, the successively bonds are break and formed transferring the squeezing effect due to extra layer and creates a permanent shear amongst the atoms.

5) The atoms rearrange themselves so as to nullify the squeezing of atoms and layers get separated.

Screw Dislocation

1) When a layer of crystal structure is partially slides over other creating shear between layers is known as screw dislocation.

2) The layer slide over other in spiral form making shape of it like screwing form so it is named as screw dislocation.

3) The burger vector measure the intensity of dislocation and it is parallel to plane of dislocation.

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