Crystal Defects

Abstract

A crystal with a volume of 1 cm³ will contain about 10²³ atoms. Lattice theory requires in principle that all of these atoms occupy a regular lattice. The array of atoms must conform to one of the 230 space groups. The equivalent points of a position of a space group must be fully occupied by atoms of the same type. This theoretical model is only achieved conceptually, by an ideal crystal.

The observation of a large number of crystals will show that they in fact have cracks and fissures, and that crystal faces are often not really flat. At cleavage surfaces, crystalline domains are often displaced with respect to one another. Inclusions occur in crystals, which may themselves be crystalline, liquid or gas. In practice, a real crystal deviates considerably from the ideal model described above.