What is the value of z for a body-centred unit cell?

A BCC unit cell has atoms at each corner of the cube and an atom at the centre of the structure. The diagram shown below is an open structure. According to this structure, the atom at the body centre wholly belongs to the unit cell in which it is present.

  • In BCC unit cell every corner has atoms.
  • There is one atom present at the centre of the structure.

Number of Atoms in BCC Cell:
Thus, in a BCC cell, we have:

8 corners × 1/8 per corner atom = 8 × 1/8 = 1 atom
1 body centre atom = 1 × 1 = 1 atom
Therefore, the total number of atoms present per unit cell = 2 atoms.

Since the number of atoms for a body-centred cubic unit cell is 2, z = 2


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