Question

a) Calculate the packing efficiency in simple cubic lattice?
b) What is Frenkel defect? Give an example?

Answer 1

a) Packing efficiency in simple cubic lattice:
$\text{Packing efficiency}$ $=\frac{\text{volume of one atom}}{\text{volume of cubic unit cell}}\times 100\%=\frac{\frac{4}{3}\pi r^3}{8r^3}\times 100=52.36\%\approx 52.4\%$b) A Frenkel defect: Frenkel disorder is a type of point defect in a crystal lattice. The defect is created when an atom or smaller ion (like cation) leaves its place in the lattice creating a vacancy and becomes an interstitial by placing in a nearby location. Frenkel defects are exhibited in ionic solids with a large size difference between the anion and cation.

Some examples of solids which exhibit Frenkel defects:

zinc sulfide,

silver(I) chloride,

silver(I) bromide (also shows Schottky defects),

silver(I) iodide.