A point defect is a localized disruption or irregularity in the otherwise perfect arrangement of atoms in a crystal lattice structure. It involves one or a few atoms and does not extend in space beyond a very small region, typically around one to two atomic diameters, making it a zero-dimensional (0-D) defect
. Point defects occur when:
- One or more atoms are missing from their normal lattice sites (vacancies).
- Atoms are displaced from their lattice sites to interstitial positions (interstitial defects).
- Foreign atoms occupy lattice or interstitial sites (impurity defects).
- An atom leaves its site and occupies an interstitial site, creating a vacancy-interstitial pair (Frenkel defect)
Common types of point defects include:
- Vacancy defect: A lattice site is unoccupied by an atom that should be there, also called a Schottky defect in ionic solids when vacancies occur in pairs
- Interstitial defect: An atom occupies a normally unoccupied site in the lattice, often an impurity or a displaced atom
- Frenkel defect: A combination of vacancy and interstitial defect where an atom moves from its lattice site to an interstitial site
- Impurity defect: Foreign atoms replace or occupy interstitial sites in the crystal lattice, altering its properties
Point defects are the smallest and simplest type of crystal imperfections but can significantly affect the material's physical and chemical properties, such as electrical conductivity and diffusion
