It is the simplest geometrical pattern which, by repeating itself indefinitely, constitutes a crystalline lattice. It is characterized
1) by the lengths $ a, b $ and $ c $
2) the angles $ \alpha, \beta $ and $ \gamma $
3) the arrangement of atoms:
- to the 8 vertices: primitive unit cell
- to the 8 vertices and centers of both bases: base-centered unit cell
- to the 8 vertices and the center of the unit cell: center unit cell
- to 8 vertices and centers of faces and bases: face-centered unit cell
Auguste Bravais 1811-1863
There are 7 primitive elemental unit cells which give rise to 14 Bravais unit cells.
By reproducing indefinitely in all three dimensions, they give rise to the → 7 cristal systems :