Phenomenological Model for Pyroelectric Effects of Nano Graded Ferroelectric Films

In order to improve the pyroelectric properties of nanograded ferroelectric films (NGFF), and provide a theoretical reference for practical applications, the generalized Ginzburg-Landau-Denvonshire (GLD) theory is adopted to investigate the pyroelectric properties of the NGFF. A function is introduced to characterize the local structure in nanograded films. Influence of the local structure, film thickness and external electric field on the polarization distribution and pyroelectric properties are mainly discussed. The numerical results show that parameterand film thickness are two very important factors that influence the film properties, larger values lead to smaller spontaneous polarization and lower pyroelectric peak. Different directions of the external electric field can lead to greatly different effects on pyroelectric behaviors, whose effects is to expand the working temperature region, or else, change the order of phase transition.