The unit cell is a structural component that, when repeated in all direction, resaults in a macroscopic crystal. Structures of the 14 possible crystal structures (Bravais lattices) are shown in Figure 7.1.Several different unit cells are possible for some structures; the one used may be chosen for convenience,depending on the particular application. The atoms (or ions) on the corners, edges, or faces of the unit cell are shared with other untill cells as follows: