Dielectric Characteristics and Layer Periodic Effects of Ferroelectric Superlattice BaTiO_(3)/SrTiO_(3)

A pseudospin-phonon coupled model in double-time Green's function theory has been developed to investi- gate the dielectric susceptibility of the ferroelectric-dielectric superlattice BaTiO_(3)/SrTiO_(3) (BTO/STO). As the pseudospin-pseudospin and pseudospin-phonon interactions increase, the dielectric susceptibility changes from a narrow shape into the strong and broad shape with the peak shifting to a higher temperature region. With increasing pseudospin-phonon interaction in the BTO layer and at smallpseudospin-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 the high-temperature region covering the tetragonal-cubic transition temperature of barium titanate. A critical period of 10/I0 in the BTO/STO superlattice has been obtained, which is in good agreement with the experimental data of 40A, for ten unit cells.