Question

Antifluorite structure is derived from fluorite structure by

• A. Heating fluorite crystal lattice
• B. Subjecting fluorite structure to high pressure.
• C. Interchanging the positions of positive and negative ions in the lattice.
• D. None of these

Answer 1

The correct option is C Interchanging the positions of positive and negative ions in the lattice.

$Ca{F}_2$ has fluorite type structure.
In fluorite structure, $C{a}^{2+}$ ions forms the ccp arrangement. Thus, it occupies the corners and face centres of the cubic unit cell. Then, $F^{-}$ ions occupy all the tetrahedral voids of ccp lattice.

$N{a}_{2}O$ has antifluorite type structure.
In this $O^{2-}$ ions forms the ccp arrangement and $N{a}^{+}$ occupy all the tetrahedral voids.

Thus, the only difference between the two structure is the position of negative and positive ions.

Thus, interchanging the position of positive and negative ions will result conversion from fluorite to antifluorite structure or from antifluorite to fluorite structure.