## 1.3 Defects, Materials and Products

### 1.3.1 General Classification of Defects

| Crystal lattice defects (defects in short) are usually classified according to their dimensions. Defects as dealt with in this course may then be classified as follows:
| 0-dimensional defects
|  | We have "point defects" (on occasion abbreviated PD), or, to use a better but unpopular name, "atomic size defects" .
|  | Most prominent are vacancies (V) and interstitials (i). If we mean self-interstitials (and you should be careful with using the name interstitials indiscriminately), these two point defects (and if you like, small agglomerates of these defects) are the only possible intrinsic point defects in element crystals.
|  | If we invoke extrinsic atoms, i.e. impurity atoms on lattice sites or interstitial sites, we have a second class of point defects subdivided into interstitial or substitutional impurity atoms or extrinsic point defects.
|  | In slightly more complicated crystals we also may have mixed-up atoms (e.g. a Ga atom on an As site in a GaAs crystal) or antisite defects
| 1-dimensional Defects
|  | This includes all kinds of dislocations; for example:
|  | Perfect dislocations, partial dislocations (always in connection with a stacking fault), dislocation loops, grain boundary and phase boundary dislocations, and even
|  | Dislocations in quasicrystals.
| 2-dimensional Defects
|  | Here we have stacking faults (SF) and grain boundaries in crystals of one material or phase, and
|  | Phase boundaries and a few special defects as e.g. boundaries between ordered domains.
| 3-dimensional Defects
|  | This includes: Precipitates, usually involving impurity atoms.
|  | Voids (little holes, i.e. agglomerates of vacancies in three-dimensional form) which may or may not be filled with a gas, and
|  | Special defects, e.g. stacking fault tetrahedra and tight clusters of dislocations.
| If you understand German, you will find an elementary introduction to all these topics in chapter 4 of the "Materialwissenschaft I" Hyperscript

© H. Föll (Defects - Script)