When two more spheres are placed adjacent to the single sphere placed in layer b, the central point between these six spheres (3 from layer a and 3 from layer b) is referred to as an octahedral hole and is shown in figure 17.4
a)
b)
Figure 17.4 Octarahedral holes.
There is an upper limit to the size of the sphere that can be placed in these holes and we will take this up after calculating the packing fraction.
