  Many materials exhibit nanoscale phase separation, when inside the host
thermodynamic phase there arise nanosize embryos of another thermodynamic
phase. A prominent example of this phenomenon is provided by ferroelectric
materials. The theoretical description of such phase heterogeneous materials is
quite challenging, since they are essentially nonuniform, the nonuniformity is
random, and often they are quasiequilibrium, but not absolutely equilibrium. An
approach is suggested for the theoretical description of phase separated
ferroelectrics, consisting of a ferroelectric matrix with nanoscale
paraelectric inclusions. The properties of the heterophase ferroelectrics are
studied.
