Relationship between ionicity, ionic radii and order/disorder in complex perovskites

Analysis of the available structural data on the ordering of B-site cations in complex perovskites with the general formula A(2)B(V)B(III)O(6) has been performed. Low ionization potentials of B-site cations are found to promote their ordering. A linear relation between the order-disorder phase transition temperature T-t and the sum of ionization potentials of B-site cations is observed in (Pb2BBO6)-B-V-O-III perovskites. It can be used for predicting T-t of other complex compounds. The electronegativity equalization method (EEM) has been used to determine the effective ionic charges and the ordering energies. The results of simulation support the correlation disclosed. In contrast to what was previously postulated, the influence of the size of B-site cations on the ordering is shown to be negligible. The determining driving mechanism responsible for the ordering is found to be the electrostatic, rather than the elastic, interactions between the B-site ions. (C) 2000 Elsevier Science Ltd. All rights reserved.