Structure of a mixed oxide is cubic close packed (CCP). The unit cell of mixed oxide is composed of oxide ions. One fourth of the tetrahedral voids are occupied by divalent metal A and the octahedral voids are occupied by a monovalent metal B. The formula of the oxide is

Oxide ion form CCP Effective number of oxide ions =8 corners X 1/8 per corner atom share + 6 faces X 12per face center atom share                                                  = 4 O-2number of tetrahedral voids=8 and number of octahedral voids = 4Effective number of A  divalent ions =14X number of tetrahedral voids =14X 8= 2 AEffective number of B mono valent ions = 4 BFormula of CCP unit cell = A2B4O4=AB2O2