Dielectric characteristics and layer periodic effects of ferroelectric superlattice BaTiO3/SrTiO3

A pseudospin-phonon coupled model in double-time Green's function theory ha s been developed to investigate the dielectric susceptibility of the ferroe lectric-dielectric superlattice BaTiO3/SrTiO3 (BTO/STO). As the pseudospin- pseudospin and pseudospin-phonon interactions increase, the dielectric susc eptibility changes from a narrow shape into the strong and broad shape with the peak shifting to a higher temperature region. With increasing pseudosp in-phonon interaction in the BTO layer and at small pseudospin-pseudospin i nteraction in BTO layer, the dielectric susceptibility was sensitively adju sted around the transition temperature of strontium titanate, and at large pseudospin-pseudospin interaction in the BTO layer, the dielectric suscepti bility was increased in the high-temperature region covering the tetragonal -cubic transition temperature of barium titanate. A critical period of 10/1 0 in the BTO/STO superlattice has been obtained, which is in good agreement with the experimental data of 40 Angstrom, for ten unit cells.