What does the Burgers vector represent?

• A. The energy of the dislocation
• B. The velocity of dislocation glide
• C. The slip plane orientation
• D. The magnitude and direction of lattice distortion from a dislocation

Answer: (D)

It is a vector that captures the magnitude and direction of the lattice distortion produced by a dislocation. You can see this by imagining drawing a closed loop around the dislocation in the crystal lattice. In a perfect crystal, tracing a loop would bring you back to the starting lattice site. Around a dislocation, you don’t quite land on the same site; you’re offset by a fixed translation, and that offset is the Burgers vector. It tells you how much the lattice is effectively shifted due to the presence of the dislocation, both in size and in which way it’s shifted.

This vector is a property of the dislocation and the underlying lattice; it often corresponds to a lattice translation vector and typically has a magnitude on the order of the lattice constant. It is not the energy of the dislocation, nor its glide velocity, nor the orientation of the slip plane—that information relates to forces, motion, and geometry of slip, while the Burgers vector is purely a geometric measure of the distortion the dislocation imposes. For context, in an edge dislocation the Burgers vector lies in the slip plane and is perpendicular to the dislocation line, while for a screw dislocation it runs parallel to the line, illustrating how the same concept describes different dislocation characters.