Question

A unit cell of a cube in which there are A atoms at the corners and B atoms at the face centres and A atoms are missing from 2 corners of each unit cell.What is the simplest formula of the compound ?

Answer 1

A atoms are at the corners and B atoms are at the face centres. Therefore, the given compound has an fcc lattice structure.
If two A atoms are missing,
contribution from corner atoms = 6 x 1/8 = 3/4
Contribution of B atoms at face centres = 1/2 x 6 = 3
Formula of the compound = A_3/4B₃
Simplest formula = A₃B₁₂ = AB₄