Calculate the number and position of tetrahedral and octahedral voids in a $ccp$ or $fcc$ structure.

(N/A) - $(A)$ Tetrahedral Voids: In a $ccp$ or $fcc$ lattice,the unit cell is divided into $8$ small cubes. Each small cube has atoms at alternate corners. If these are joined,they form a regular tetrahedron. Thus,there is one tetrahedral void in each small cube,totaling $8$ tetrahedral voids.
- In a $ccp$ structure,there are $4$ atoms per unit cell. Since the number of tetrahedral voids is twice the number of atoms,there are $4 \times 2 = 8$ tetrahedral voids.
- $(B)$ Octahedral Voids: There is one octahedral void at the body center of the cube. Additionally,there are octahedral voids at the center of each of the $12$ edges. Each edge center is shared by $4$ adjacent unit cells,so the contribution of each edge-centered void to a single unit cell is $\frac{1}{4}$.
- Total octahedral voids = $1$ (body center) $+ 12 \times \frac{1}{4}$ (edge centers) $= 1 + 3 = 4$.