In a unit cell atoms of the type ‘A’ are arranged in F.CC. pattern, and ‘B’ type atoms occupy alternate tetrahedral voids. The formula of the compound is

Number of effective atoms of A = 6×12 + 8 ×18= 4Number of tetrahedral voids = 2 n = 2 ×4 = 8 Alternative tetrahedral voids are occupied by B, number of B atoms = 4 Formulae = A4B4 = AB