Chapters / Chapter 1 · Solid state / Topic 11 of 14

There are different types of imperfection, such as point, surface and volume imperfections. Point defects are zero-dimensional, occurring at a single lattice site; extended defects may be one, two or three-dimensional (for example a stacking fault). Defects can also be classified as intrinsic and extrinsic.

Intrinsic defects (Schottky and Frenkel defects) occur in the pure crystal, while extrinsic defects originate from impurities present in the crystal. Defects can largely influence physical properties such as mechanical strength, electrical conductivity, colour and chemical reactivity. In ionic crystals only point imperfections are important.

Point imperfections

Point imperfections are very often referred to as zero-dimensional imperfections. They are localised in point-like regions and may arise due to:

1. A vacancy in a lattice site.
2. A substitutional impurity.
3. Occurrence of a constituent ion in an interstitial space.
4. Non-stoichiometric proportions of the constituent ions.