The effects of surface transition layers on the phase diagrams and the pyroelectric properties of ferroelectric thin films

By taking into account surface transition layers STLs and single surface transition layer SSLs (introduced for comparison), the phase-transition and pyroelectric properties of ferroelectric thin films described by the transverse Ising model (TIM) are discussed in the framework of the effective-field theory, based on the probability distribution technique. We discuss an N-layer film of simple cubic symmetry with nearest-neighbor exchange interaction in which the exchange-interaction strength is assumed to be different from the bulk values in surface layers. We derive and illustrate expressions for the phase-transition and pyroelectric profiles. We demonstrate that the phase transition depends more strongly on intra-layer interaction than inter-layer interaction and the ferroelectricity of a film will disappear at a critical STL thickness if the intra-layer and inter-layer interactions are weak. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim