Theoretical Investigation On Polarization And Dielectric Properties Of Ferroelectric Bilayer Film With Interfacial Coupling

Compared with the bulk material , ferroelectric thin films have unique characteristics, such as piezoelectric, pyroelectric, electro-optic, acousto-optic, photorefractive effect and other excellent properties, the preparation of ferroelectric thin film technology has been widespread concern and attention. With the technology and the deepening of research, people want to prepare a small, high density, and low energy loss ferroelectric thin film devices. However, due to the process of preparation of impurities, defects, interface, interface lattice mismatch induced stress, as well as the interface between the effect of different components and other factors, iron and engineering properties of thin films corresponding body produces a discrepancy between the materials. Through many research and numerous published studies analyzing the results, we believe that as between the ferroelectric film and electrode, the interface between different materials, the original stress and defects exist in the original. The reason that the experiment with individual differences is the distribution of stress and defects is different. Their presence will cause differences in film structure, the result will be generated near the film surface or interface structure of the transition zone, it is this structural transition zone on the nature of ferroelectric thin films had a big impact and may even lead to iron films no physical effect. So researching on the surface or interface interlayer effectnot only has theoretical significance but also has very practical research value.In this thesis, under the mean field approximation, we use the transverse field Iing model to study the polarization of the ferroelectric bilayer distribution, phase transition temperature and dielectric properties of the surface transition layer effect. So far, all the published literature have not considering the difference between the surface and internal structure in the ferroelectric bilayers. actually the difference between the surface and internal structure of different materiAls is very large. as the surface of impurities, defects, or stress, strain, it will increase the surface structure of the disorder, and this surface effect, not only between the outermost surface, but also affect the certain depth below the surface. Therefore, we introduces the concept of the surface transition layer in ferroelectric bilayers for the first time. In the theory of transverse field Ising model theory, we introduce two kinds of material within the surface transition layer middle layer pseudo-spin and pseudo-spin interaction function, J_a (m ),J_ae (m )And J_b (m),J_be (m), and the two materials a and b in the surface transition layer cross-field tunneling frequency change functionΩ_as andΩ_bs to describe the surface ferroelectric transition layer and the internal structure of bilayer uneven features. The promoting of transverse field Iing model may promote the study of ferroelectric bilayers. We have the following main conclusions:1. The nature reason that the property of the ferroelectric bilayer is different from the material is the existing of the ferroelectric bilayer surfAce transition layer. The very important factor affect the ferroelectric polarization properties of bilayer membrane and dielectric properties is the thickness of the surface transition layer .The surface transition layer can not be ignored in substrate and the electrode in the study of ferroelectric bilayer.2. The surface transition layer can make the phase transition temperature of the ferroelectric bilAyer below the materials ,. With the increase of the surface trAnsition layer and the decrease of surface of the pseudo-spin interaction of the tunneling J S or the increase of the frequencyΩs, it will make the phase transition temperature of the ferroelectric– paraelectric below and dielectric peaks move to lower temperature.3. The impact of surface transition layer in the middle of two nearest neighbor layer pseudo-spin interaction coefficient on the ferroelectric properties of bilayer membrane is more significant than the surface transition layer intermediate between the two nearest neighbor pseudo-spin interaction coefficient.4. In the form of two ferroelectric bilayer materials, for the pseudo-spin interaction strength of the material, the impact of the changes of its structural in the surface transition layer on ferroelectric bilayer plays a decisive role.5. The interface between the coupling coefficient of the paper industry (j> 0) benefit system in the ferroelectric phase.This paper is in the framework of mean field approximation theory. We reseaarch the ferroelectric polarization properties of bilayer membrane and dielectric properties.To some extent, the results and conclusions have enriched the field of ferroelectric bilayers research content, and may have some guidance to the experimental work, but a lot of work remaining to be studied further.