Question

Find the size of largest sphere that will fit in octahedral void in an ideal FCC crystal as a function of atomic radius r.

• A. $0.155r$
• B. $0.225r$
• C. $0.414r$
• D. $0.732r$

Answer 1

Answer: (C)

$0.414r$

Let the radius of the octahedral void be $a$ and the spheres be $r$ .
In the adjoining figure it can be seen that,
$2r\sqrt{2}=2r+2a$
$⟹a=0.414r$.