Question

In the cubic close packing, the unit cell has ________.

• A. $8$ tetrahedral voids within the unit cells.
• B. $8$ tetrahedral voids each of which is shared by four adjacent unit cells.
• C. $4$ tetrahedral voids each of which is shared by four adjacent unit cells.
• D. $4$ tetrahedral voids within the unit cell.

Answer 1

The correct option is A $8$ tetrahedral voids within the unit cells.

$\text{Location and number of tetrahedral voids in cubic close packing}\left(FCC\right)$

In a cubic close packing ($FCC$ unit cell), one corner sphere and three face spheres form one tetrahedral void. In an $FCC$ structure, two tetrahedral voids are obtained along one cube diagonal. There are four cube diagonals in one unit cell. Thus, there are eight tetrahedral voids inside an $FCC$ unit cell.