With the help of a labelled diagram show that there are four octahedral voids per unit cell in a cubic close packed structure.

In cubic close packing, each cube consists of eight small cubic components as shown in figure. Since atoms are present in corners and face centres, total atoms are:

Total atoms= atoms at face centres and atoms at corners

=8× (1/8) + 6× (1/2)=1+3 = 4

Total number of atoms = 4.

Now octahedral voids are present at Edge centres and body centre. (refer figure)

Total number of octahedral voids =

Hence proved. 4 octahedral voids are present in cubic close packing.