In the Zinc Blende () crystal structure, what is the exact fractional occupation of the tetrahedral — Solid State Chemistry Question

💡 Solution & Explanation

In the Zinc Blende (sphalerite) structure, $S^{2-}$ ions form a ccp (fcc) lattice. There are 8 tetrahedral voids per unit cell, but $Zn^{2+}$ ions occupy only the alternate (non-adjacent) tetrahedral voids to minimize electrostatic repulsion. Thus, exactly half ($\frac{1}{2}$) of the tetrahedral voids are occupied, giving 4 $Zn^{2+}$ ions per unit cell.