Investigation On Ferroelectric Properties And Ferroelectric Photovoltaic Effect Of Bismuth Ferrite-based Films

Ferroelectric materials have attracted extensive attention due to their unique properties.They have been used in many fields such as supercapacitors,optical waveguides,piezoelectric sensors and memory storage.As one of the most typical ferroelectric materials with ABO₃ perovskite structure,BiFeO₃（BFO）has been extensively studied for its electrical,magnetic and optical properties.The theoretical polarization of BFO is larger than 100μC/cm².However,in practice,due to the existence of defects such as oxygen vacancy and the generation of hybrid phase in the preparation process.The leakage current increases,leading to a far smaller polarization than the theoretical value.And its application value is greatly reduced.Therefore,BFO-based ferroelectric films were prepared by sol-gel method.The leakage current and the ferroelectric properties were improved by element substitution.Optical properties of films have also been studied.The specific work is described as follows.Firstly,BFO films were prepared by sol-gel method.Replacing Bi with Ho,and replacing Fe with Mn,preparation of the Bi_0.85Ho_0.15Fe_0.95Mn_0.05O₃（BHFMO）films.Electrical and optical properties were characterized.After doping with Ho and Mn,the leakage current of the films is reduced,thus the polarization of the film is improved and the ferroelectric properties of the film are improved.On this basis,the photovoltaic effect of BFO and BHFMO films was studied.By measuring the reflectance spectrum,spectral response and J-V curves of films,it is found that the improved ferroelectric property and reduced band gap can promote the photovoltaic performance of BFO films.Secondly,the films that replacing Bi with Pr and Dy,replacing Bi with Ce and Dy were prepared by the same method.The properties of leakage,ferroelectricity and dielectric of the films were characterized.The effects of different displacement ratios on ferroelectric properties of thin films were studied.When Ce and Dy are in a certain proportion,the film leakage current remains stable,the shape of hysteresis loop is good,and the remanent polarization is large.The relative dielectric constant remains stable with frequency.However,Pr and Dy could not improve the ferroelectric properties of BFO films,and the relative dielectric constant is unstable.The reason for this difference is analyzed.This is because Ce and Pr have different electron polarizability.