Impact of layer defects in ferroelectric thin films

Based on a modified Ising model in a transverse field we demonstrate that defect layers in ferroelectric thin films, such as layers with impurities, vacancies or dislocations, are able to induce a strong increase or decrease of the polarization depending on the variation of the exchange interaction within the defect layers. A Green function technique enables us to calculate the polarization, the excitation energy and the critical temperature of the material with structural defects. Numerically we find the polarization as a function of temperature, film thickness and the interaction strengths between the layers. The theoretical results are in reasonable accordance with experimental data of different ferroelectric thin films