We develop a formalism to model configurational thermodynamics in ionic systems with multiple anion and cation species. Because cations and anions can be partitioned into two interacting sublattices that do not exchange species, the dimensionality of configuration space is significantly reduced. The result is a model applicable to many important problems in ionic systems. Here we show that the effect of an order-disorder transition in one sublattice on the other depends on how the symmetry is changed through the transition, as well as on the strength of the interactions.

• Received 12 May 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.2272