Theoretical Study On Pyroelectricity Of Composite Ferroelectric Thin Film

In this thesis the author studies the influence of inhomogeneous structure on properties of ferroelectric film. In fact, many surface factors existing in thin ferroelectric film, for example impurities, defects and surface or interface stresses and so on, are the cause of leading up local inhomogeneous structure. It is just inhomogeneous structure that produces the inhomogeneous spontaneous polarization distribution which gives rise of many different phenomena from bulk materials, such as size effect. These novel phenomena can be considered as the bases of the device applications, such as computer's FDRAM, ultrasonic devices, acoustic surface devices and photoelectric devices. Therefore, to study the influence of inhomogeneous structure on ferroelectric film is practically important and also has fundamental theoretical value. So far as we know, seldom papers about the influence of inhomogeneous factors on system properties has been reported because of the complexity of studying theoretically. Based on above consideration the author choices the subject.Within the framework of thermodynamic phenomenological theory, ageneralized GLD free energy has been developed to describe the second--orderphase transition for CFTF. We have found local structure leads to descent of high spontaneous polarization and ascent off low spontaneous polarization,At the same temperature polarization along the distribution of film thickness direction indicates weak ferroelectric reaction with high Curie temperature of local structure and vice versa, Through the numeric computation we investigated the polarization and pyroeleetricity dependence of local structure, temperature , applied electric field and thickness of CFTF. In the first chapter of this paper, we introduced the basic concept,the sorts,the theoretical investigate ways,the fabrication,the application and the problems which is appeared in investigating, we also introduce the aim and primary content;In the second chapter of this paper, we introduced the ferroelectric thin film are used to calculating the transmission spectrum and band structure;Third chapter we introduced the emphasis thing, it will cause the later things;the Fourth chapter and Fifth chapter is the most important part .in these we can learn about the finish though severe ideas and we can learn the ferroelectric thin film .In complex ferroelectric thin film, because of the two gradient film field phase-transition temperature is enhanced,the expense of the lessening of pyrelectric coefficient compensates far the expansion of working temperature region. Applied filed is big enough to coverup transition of CFTF. In transition tcmporatuxe region polarization curves can be fatten by the lessening of the thickness, however, in higher than transition temperature region pyroelectric Coemcient increases with the augment of thickness of thin films, but in temperature region lowered than CFTF transition temperature pyroelectric coefficient with relative thinner thickness descend faster.In complex ferroelectric thin film, the action of depolarization field is so notable that it makes spontaneous polarization tending towards homogeneous distribution. This effect will be more noticeable for ultra-thin ferroelectric film. Besides, average polarization changes linearly with film thickness. The author also thinks that some properties of thin ferroelectric gradient film are close to that of bulk ferroelectric material with the structure at some position in film. So thin ferroelectric gradient film has no advantage when these properties are used. But in practical application, ones require a film to work steadily under room temperature. If it is difficult to process this bulk ferroelectric to satisfy the above requirement, thin ferroelectric gradient film is the ideal and realistic choice,and it good for ferroelectric thin film.Through theory count,we get the conclusions above ,we hope it will play a important role of theoretical study on ferroelectric thin film in the future and lead to a certain promote effect.