Question
If the radius of the octahedral void is r and radius of the atoms in close packing is R, derive relation between r and R.
Solution
An octahedral void is shown in Fig. Though an octahedral void is surrounded by six spheres, only four are shown. The spheres present above and below the void are not shown. Let us assume that the edge length of the unit cell is a cm and raius of octahedral void is r and the radius of sphere is R.


In the given figure, let an sphere having centre ‘O’ is fitted in the octahedral void.
As given, radius of the sphere fitted in the octahedral void = r
And radius of the atoms in close packing = R