Question

Which of the following statements is/are true regarding $L{i}_{2}O$ (anti-fluorite structure) ?

• A. $r_{L{i}^{+}}+r_{O^{2-}}=\frac{\sqrt{3}a}{4}$
• B. oxide ions forms the fcc lattice
• C. cations are present in all the tetrahedral voids
• D. All of the above

Answer 1

The correct option is D All of the above

In antifluorite structure, anions form the fcc lattice while cations occupies all the tetrahedral voids.
Each body diagonal of fcc lattice has two tetrahedral void.
Thus, cation and anion are touching each other along body diagonal of the each terahedral site of the lattice.
Let the edge length of unit cell be "a".
$\text{Body diagonal length}=2(r^{+}+r^{-})=\frac{\sqrt{3}a}{2}$
So,
$r^{+}+r^{-}$ = $\frac{\sqrt{3}a}{4}$

Thus, statement (a), (b) and (c) are correct.