Question

4) Define the Burger vector and explain what is its meaning and what it quantifies. The relative orientation between the dislocation line and the Burger vector helps to classify linear defects in crystals, explain

Answer 1

The burger vector is a term used usually to denote dislocations in a crystal lattice. it is nothing but the measure of distortion or deformation which usually occurs in the presence of a line defect.

Thus, burger vector can be defined as a unit vector of the lattice, if the dislocation is a unit dislocation. It is named after Dutch physicist Jan burgers and is denoted by the letter 'b'. This vector denotes both the magnitude and direction of the distortion in the crystal lattice.

This vector can be clearly understood by first considering a perfect crystal structure that does not contain any dislocations. In this crystal structure, a rectangle is drawn . After drawing a rectangle within this crystal, the dislocation can be introduced. This distortion affects both crystal geometry and the drawn rectangle.

This can be over come by calculating the magnitude and direction of burger vector by drawing a burger circuit.

This circuit is made around the dislocation line of the crystal lattice. This obtained circuit is then transferred into ideal crystal. The burger vector is usually characterized by noticing the extra inter-atomic spacing which is needed to close the loop.

All crystal structures are not perfect; which means the atoms in the crystal structure are not in a proper order. Depending upon the orientation of the burger vector, the type of defect int the crystal can be identified.

Crystals have several linear defects.

In edge dislocations, the burger vector is perpendicular to the dislocation line whereas in screw dislocation, the burger vector is parallel to the dislocation line. Thus, it can be seen that for different dislocations orientation of the burger vector varies. Hence, burger vectors can be used to classify the linear defects in the crystal.