Interfacial coupling in ferroelectric superlattices

A phenomenological theory is presented to describe ferroelectric superlattices with first-order phase transitions. Static properties including the Curie temperature, spontaneous polarization and dielectric susceptibility are discussed with model parameters appropriate to BaTiO₃/PbTiO₃. When the strength of interfacial coupling is weak, a size-driven phase transition still occurs with decreasing periodicity of the superlattice. The properties depend sensitively on the interfacial coupling and the thicknesses of the component slabs. The dielectric susceptibility is very different from the result for a simple series connection, especially in the high-temperature range, and can be designed flexibly by varying the layering sequence.