Define Burgers vector ?

 The Burgers vector is a fundamental concept in materials science and crystallography that describes the magnitude and direction of lattice distortion caused by a dislocation in a crystal.

In simpler words:

• A crystal is made of atoms arranged in a repeating pattern.

• If there is a dislocation (a kind of defect), the atoms are displaced from their regular positions.

• The Burgers vector tells you how far and in which direction the atoms have shifted due to that defect.

Key points:

1. Symbol: Usually represented by $\mathbf{b}$.

2. Units: Length (meters, nanometers, or Ångströms).

3. Determination: It is found by drawing a Burgers circuit — a closed loop around the dislocation — and measuring the closure failure.

4. Types:

   • Edge dislocation: Burgers vector is perpendicular to the dislocation line.

   • Screw dislocation: Burgers vector is parallel to the dislocation line.

   • Mixed dislocation: Burgers vector is at an angle to the dislocation line.

In short:
The Burgers vector is a measure of the permanent atomic shift caused by a dislocation, and it’s essential for understanding mechanical properties like strength and ductility.

If you want, I can also draw a simple diagram showing how the Burgers vector is measured for edge and screw dislocations.