A model to determine the structural stability and cation configuration of Aurivillius phases is presented. Structural stress caused by elastic coupling between the (M2O2) and (A(n-1)B(n)O(3n+1)) substructures that form the phase and the electrostatic attraction forces between them are considered. The model suggests that the cation exchanges observed in these substructures result from a balance between the cohesive electrostatic energy and the disruptive elastic coupling energy. The model explains and predicts the cation configuration of Aurivillius phases of type (Bi2-xPbxO2)(PbyBi1-y)(n-1)BnO3n+1, where the cation exchange between M and A sites is of Bi3+ <-> Pb2+ type. The PbBi2Nb2O9 phase is taken as a case study. This material has been studied quantifying this cation exchange and several theoretical models have been developed to explain the phenomenon. The cation equilibrium configuration determined by the present model is much more accurate than previous studies. Furthermore, a precise explanation of this phenomenon is provided. (c) 2012 Elsevier Ltd. All rights reserved.