Theoretical study of dielectric susceptibility in ferroelectric thin films

Based on a pseudospin-phonon interaction model dielectric susceptibility in ferroelectric thin films was studied by using double-time Green's functions method. The dielectric susceptibility peak shifts up to higher temperature with increasing the pseudospin-phonon coupling. Critical pseudospin-phonon couplings were obtained. Below the critical coupling Curie temperature for the film is lower than that for the bulk and the transition temperature for the film decreases with decreasing the film thickness: above the critical coupling Curie temperature for the film is higher than that for the bulk and the transition temperature for the film increases with decreasing the film thickness. (C) 2001 Elsevier Science B.V. All rights reserved.