The Study Of The Structural Relaxation Of Ferroelectric Thin Films

Ferroelectric materials appeared several decades ago and the technology of ferroelectric thin films began in the seventies of twenty century. With the development of film preparing technology, this new kind of function material is extensively applied in many fields such as electronic technology, laser technology, infrared detection and other aspects of engineering technology.Due to the restrictions of the preparing technologies, there will be impurities, defects, interfacial stress in the surface layer of the ferroelectric thin film, it made the thin film show a non-uniform system in the vertical direction on the surface and resulting in the uneven distribution of spontaneous polarization. This surface layer is called the imperfect surface layer. It makes the properties of ferroelectric thin film different from the three-dimensional ferroelectric and the thin film is more practical value.The practical application of ferroelectric thin film has a variety of structures, but the main structure in the form is caught in two electrodes. The electrode can be Metal and semiconductor material. Because the reality of the current is ac electric field generally. Therefore, a single discussion of the properties of DC electric field can no longer meet the people's needs. This paper is to study the properties of ferroelectric thin film which contains imperfect surface layer in AC electric field.In the study, we proceed from the soft mode theory in mean-field approximation. Taking into account the second-order ferroelectric phase transition, we discuss the specific inductive capacity correlative with the frequency of the external electric field and the phase transition temperature in AC electric field.Through theoretical calculation and graphical analysis, the existence of the imperfect surface layer can raise the specific inductive capacity, but the phase transition temperature has decreased with the increase of the imperfect surface layer's thickness. The ferroelectricity can be seen only after considering the interaction, but when the interaction is strong, the specific inductive capacity is high and the phase transition temperature is low which is detrimental to the stability of the ferroelectric phase. For our investigation, the frequency will be real only after considering the effects of non-harmonic. With the damping coefficient's increasing, the specific inductive capacity distribution curve correlative with the frequency of the external electric field shows a wide peak. The scope of the phase transition temperature becomes larger which makes the system more unstable.In AC electric field, both the real part and the imaginary part of the specific inductive capacity will change with the temperature's variation. With the increase of the frequency, the dielectric susceptibility will become larger and the phase transition temperature will be lower. When the frequency reaches a certain value, polarization will appear reversal.Through theoretical investigations, we have concluded that changing parameters will influence the specific inductive capacity. It points out that how to get the ferroelectric thin film which has the larger specific inductive capacity, the higher phase transition temperature and the small dielectric dissipation through controlling experimental conditions. It's good for preparation the ferroelectric thin film in experiment. It provides the theoretical foundation in order to get the better experimental data.