Order-disorder transition in (A'A'')BO3 and A(B'B'')O-3 complex perovskite crystals

A criterion of ordering was given in an earlier paper for A(B'B '')O-3 crystals with B' and B '' ions having a charge difference, It has been extended in this paper to (A'A '')BO3 crystals and to the cases where the cations have the same valence. The formulae of the effective interaction energy parameter J in (A'A '')BO3 and A(B'B'')O-3 are deduced separately, considering the interaction between ions to be a sum of the Coulomb interaction and Lennard-Jones overlap interaction. When the charge difference Delta q not equal 0, the Coulomb energy difference between the ordered and disordered states caused by the charge difference is the main driving force of ordering. When Delta q = 0, the overlap interaction term becomes important.