Topic: Cubic System

Cubic System

Cubic System

Number of Atoms in a unit Cell

Primitive cubic unit cell has atoms only at its corner.

In all, since each cubic unit cell has 8 atoms on its corners, the total number of atoms in one unit cell is 8x1/8 = 1 atom.

Body-Centered Cubic Unit Cell

body-centred cubic (bcc) unit cell has an atom at each of its corners and also one atom at its body centre. Thus in a body-centered cubic (bcc) unit cell:

(i) 8 corners 1/8 per corner atom = 8x1/8=1 atom

(ii) 1 body centre atom = 1X1= 1 atom
Total number of atoms per unit cell = 2 atoms

face-Centered Cubic Unit Cell

A face-centred cubic (fcc) unit cell contains atoms at all the corners and at the centre of all the faces of the cube. Thus, in a face-centred cubic (fcc) unit cell:

(i) 8 corners atoms 1/8 atom per unit cell= 8x1/8 = 1 atom
(ii) 6 face centered atoms x 1/2 atom per unit cell = 6x1/2 = 3 atoms

Total number of atoms per unit cell = 1+3=4 atoms