An imperfection in the regular periodic arrangement of atoms in a crystal.A lattice defect is any imperfection in the regular, repeating arrangement of atoms in a crystal. These defects can be point defects (like vacancies or interstitial atoms), line defects (dislocations), or planar defects (grain boundaries). While often considered flaws, lattice defects profoundly influence the physical properties of materials, including their mechanical strength, electrical conductivity, and optical behavior.
The concept of lattice defects emerged in the early 20th century, with the theoretical prediction of vacancies by Frenkel and Schottky in the 1920s. The role of dislocations in plastic deformation was established by Taylor, Orowan, and Polanyi in 1934.
In a perfect crystal, atoms sit at precise lattice sites, but real crystals always contain defects. For example, a vacancy is a missing atom, and an interstitial is an extra atom squeezed between regular sites. These defects disrupt the local electronic and atomic structure, creating energy levels within the bandgap of semiconductors or acting as pinning centers for magnetic domains. They also enable diffusion, which is essential for processes like doping in electronics.
Lattice defects are engineered in semiconductors to control electrical properties, in superconductors to pin magnetic flux lines, and in optical crystals like diamonds to create color centers for quantum computing. They also determine the hardness and ductility of metals.
The color of many gemstones, such as the blue in sapphires or the green in emeralds, is caused by specific lattice defects that absorb certain wavelengths of light.