Types of Units Cells
A units cell is obtained by joining the lattice points. The choice of lattice points to draw a unit cell is made on the basis of the external geometry of the crystal, and symmetry of the lattice. There are four different types of unit cells. These are,
(1) Primitive or simple cubic (sc): Atoms are arranged only at the corners of the unit cell.
(2) Body centred cubic (bcc): Atoms are arranged at the corners and at the centre of the unit cell.
(3) Face centred cubic (fcc): Atoms are arranged at the corners and at the centre of each faces of the unit cell.
(4) Side centered: Atoms are arranged at the centre of only one set of faces in addition to the atoms at the corner of the unit cell.