Question

The number of octahedral sites in fcc structure is:

• A. $1$
• B. $2$
• C. $4$
• D. $8$

Answer 1

Answer: (C)

$4$

In a cubic-closed packed structure, the number of octahedral voids at the body-centre of the cube is $1$.

$12$ octahedral voids are located at each edge and shared among four unit cells.

Therefore, the number of octahedral voids per unit cell $=12\times \frac{1}{4}+1=4$

Hence, the total number of octahedral voids is $4$.