Point defects are imperfections involving one or two atomic positions in a crystal lattice.
- Vacancy defect: An atom is missing from its normal lattice site.
- Interstitial defect: An atom (either of the host material or an impurity) occupies a position between normal lattice sites (an interstitial site).
- Substitutional defect: An impurity atom replaces or substitutes for a host atom at a normal lattice site.
This is described in the question.
- Frenkel defect (in ionic crystals): A cation leaves its normal lattice site and occupies an interstitial site, creating a vacancy and an interstitial defect simultaneously.
- Schottky defect (in ionic crystals): A pair of cation and anion vacancies.
The defect involving an impurity atom substituting for a host lattice atom is a substitutional defect.