Theoretical Investigation On Dielectric Susceptibility And Pyroelectricity Properties Of Ferroelectric Thin Film

With advancement of the preparing technologies ,the quality offerroelectric thin film has improved greatly, which intrigued extensivereseash interest of many scientists and engineers for practicalapplications in mocro-electronics technology field,photoelectrontechnology field and integration photics. Beause of the good propertiesof ferroelectricity, piezoelectricity, pyroelectricity, non-linear optics andso on, the study of the ferroelectric thin film has become the upsurge infield of the new type functional material.Due to the limitation of the preparing technologies, there aremany factors that influence the configuration of the ferroelectric thinfilm, such as impurities, defects and imperfect in crystal lattic, whichcauses imperfect surface layer in two sides of ferroelectric thin filmand makes the spontaneous polarization distribution inhomogeneous.polarization gradients in interior of ferroelectric thin film and exteriorsurface charges result in strong depolarizing field. these properties isdifferent from idea ferroelectric thin film, which makes our study ofthe ferroelectric thin film become significant.In these thesis the author applies GLD phenomenological theory,which has been proved to be one of the important and successfultheoretical approaches treating ferroelectricity. During investigationthe author studies the properities of ferroelectricity, dielectricity andpyroelectricity of ferroelectric thin film without the electrodes forsecond-order transition. through the numerical calculation weinvestigated the polarization,the average polarization, the dielectricsusceptibility, pyroelectricity, hysteresis loop and so on.During the study of properties of ferroelectric thin film, we foundthat the imperfect surface layer influence obviously on the properitiesof ferroelectric thin film. Firstly, the imperfect surface layer leads todescent of spontaneous polarization and improve the dielectricsusceptibility. Moreover, the effect is more obvious with increase oftemperature. secondly, the imperfect surface layer lowers thephase-transition temperature. Thirdly, the imperfect surface layerlowers the coercive field and makes the loop lose its squareness.Finally, the relative thickness of imperfect surface laryer and thevariation intensity of the free energy density near the surface layer aretwo main factors that influence the polarization profile. Thedepolarization field produced by the gradient of polarization in interiorof ferroelectric thin film and the exterior surface charges make thepolarization distribution more uniform. Moreover, they change thedistribution of electric susceptibility of ferroelectric thin film.The thickness of ferroelectric thin film provides a obviousinfluence on the properties of ferroelectric thin film. Thephase-trasition temperature lowers with the increasing of the thickness,when the ferroelectric thin film is thinner;But the phase-trasitiontemperature increases with the decrease of the thickness, when theferroelectric thin film is thicker. In addition to the thickness offerroelectric influences on hysteresis loop, dielectric susceptibility, thepyroelectric coefficient and the extension of working temperatureregion.External electric field provides a strong influence on thepolarization. The pyroelectric coefficient peak value lowers and theworking temperature region expands when an external field is applied.On the contrary,reverse field leads to reverse results.Equivalent multiple-domain depolarization-energy densitycoefficient influences on polarization. variety of the coefficientreflects the variety of depolarization-energy density that exteriorsurface charges applied.mOur work provides the theoretical foundation for the preparing offerroelectric thin film materials without electrodes. And we masterystherotical foundation for changing the properties of ferroelectric thinfilm ,such as raises spontaneous polarization, remnant polarization andcoereive force, widens the peak wide of pyroelectric coefficient,enhances the peak values of pyroelectric coefficient and so on.