Phase Transition Behaviours of the Spontaneous Polarization in Ferroelectric Thin Films

Abstract

Within the framework of the effective-field theory with correlations, the phase transition behaviors of the spontaneous polarization in a ferroelectric thin film with symmetrical structure have been studied in detail by the transverse field Ising model. A general expression for the phase diagram of the thin film with arbitrary exchange interactions and transverse fields is deduced through mathematical derivation. The four possible phase transition regions in the phase diagram and the Curie temperature dependence of spontaneous polarization are numerically calculated. It shows that both the spontaneous polarization and the Curie temperature can change in a different or same direction. The results are consistent with those of the usual mean-field approximation, but deviate from the Landau phenomenological theory. In addition, the temperature dependence of the spontaneous polarization in experimental facts of triglycine sulfate (TGS) thin films is also compared by the effective-field theory with correlations. Keywords-ferroelectric thin film; transverse Ising model; phase diagram; spontaneous polarization; Curie temperature