Question

Stacking of a second layer of sphere over the first layer of 2-D hexagonal close packing will result in formation of:

• A. Only tetrahedral voids
• B. Only triangular voids
• C. Only octahedral voids
• D. Both tetrahedral and octahedral voids

Answer 1

The correct option is D Both tetrahedral and octahedral voids

There are two types of voids in hexagonal packing.
1. Tetrahedral void
2. Octahedral void

Tetrahedral voids:
These voids are formed if sphere of second layer is placed over void of first layer. Connecting the spheres of the voids gives a tetrahedron shape, thus these voids are called tetrahedral voids or tetrahedral holes.

Octahedral voids:
These voids are formed if triangular void of second layer is above the first layer of voids. Connecting the spheres of the voids result in a octahedron structure. Thus, these are called octahedral voids.


Hence, stacking of layer of sphere over 2-D hexagonal close packing will result in formation of both tetrahedral and octahedral voids.