Electrostatic Model of Atomic Ordering in Complex Perovskite Alloys

We present a simple ionic model which successfully reproduces the various types of compositional long-range order observed in a large class of complex insulating perovskite alloys. The model assumes that the driving mechanism responsible for the ordering is simply the electrostatic interaction between the different ionic species. A possible new explanation for the anomalous long-range order observed in some Pb relaxor alloys, involving the proposed existence of a small amount of ${\mathrm{Pb}}^{+4\mathrm{}}$ on the $B$ sublattice, is suggested by an analysis of the model.