Is Octahedral and Tetrahedral Voids?

Tetrahedral voids are unoccupied empty spaces present in substances having a tetrahedral crystal system. Octahedral voids are unoccupied empty spaces present in substances having an octahedral crystal system. It can be found in substances having a tetrahedral arrangement in their crystal system.

How many tetrahedral voids and octahedral voids are there?

There are 8 tetrahedral voids per cell and 4 octahedral voids per cell.

Why tetrahedral voids are 2n?

Here if the number of spheres (i.e. unit cells) is said to be “n”, then the number of voids will be twice as many. So the number of tetrahedral voids will be “2n”. The void is much smaller than the sphere, i.e. it has a smaller volume.