Question

In the fluorite structure, if the radius ratio is $(\sqrt{\frac{3}{2}}-1)$, how many cations does each cation touch?

• A. $12$
• B. $8$
• C. $5$
• D. $4$

Answer 1

The correct option is A $12$

In the fluorite structure, cations have ccp lattice structure and anions occupy all the tetrahedral voids. if the radius ratio is $(\sqrt{\frac{3}{2}}-1)$, then each cation touches $12$ cations and $8$ anions.
Each corner cation touches $6$ corner cations and $6$ cations present at face centers.
Each cation at face center touches $4$ cations at corners in the plane, $4$ cations at face centers below the plane and $4$ cations at face centres above the plane.