Britannica
Sources used in this answer
How does an impurity atom fit into a crystal lattice?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
crystal
A crystal form of elemental sulfur. Sulfur has an atomic weight of about 32.06 atomic mass units (amu), which means that its molar mass is 32.06 grams.
An impurity atom fits into a crystal lattice through one of two primary mechanisms, both of which are classified as impurity defects:
- Substitutional: The foreign atom replaces a host atom at its normal lattice site. This is common when the impurity atom is of a similar size and chemical nature to the host atoms, such as germanium substituting for silicon. In ionic crystals, this process is often governed by the similarity in ionic radii; substitution is most likely when radii differ by approximately 15 percent or less.123
- Interstitial: The impurity atom is small enough to squeeze into the interstices—the voids or spaces located between the host atoms in the lattice structure.12
These impurities are not merely imperfections; they are often deliberately introduced as dopants to modify the electrical, optical, or mechanical properties of a material, such as enhancing the conductivity of semiconductors or creating the distinct colors found in gemstones.42