Question

An element (atomic weight = 50) crystallises in an fcc lattice, with a = 0.50 nm. The density of the unit cell (in gm/cc) if it contains 0.25% Schottky defects is

Answer 1

Density of a crystal decreases due to Schottky defects, effective number of atoms per unit cell in the given lattice =
4 $(1-0.25/100)$ = 3.99
$\rho =\frac{50\times 3.99}{6\times {10}^{23}\times (0.5\times {10}^{-7}{)}^3}=\frac{50\times 3.99}{6\times 125\times 0.1}=2.66$