Dielectric Characteristics and Layer Periodic Effects of Ferroelectric Superlattice BaTiO₃/SrTiO₃

A pseudospin-phonon coupled model in double-time Green's function theory has been developed to investigate dielectric susceptibility of the ferroelectric-dielectric superlattice BaTiO₃/SrTiO₃(BTO/STO). As the pseudospin-pseudospin interaction and the pseudospin-phonon interactions increase, the dielectric susceptibility changes from narrow shape into the strong-broad shape with the peak shift to higher temperature region. With increasing pseudospin-phonon interaction in the BTO layer and at small pseudospin-pseudospin interaction in BTO layer, the dielectric susceptibility was sensitively adjusted around the transition temperature of strontium titanate, and at large pseudospin-pseudospin interaction in the BTO layer, the dielectric susceptibility was increased in high temperature region covering the tetragonal-cubic transition temperature of barium titanate. A critical period of 10/10 in the BTO/STO superlattice has been obtained, which is in good agreement with experimental data of 40Å, for ten unit cells.