Preparation And Properties Of A-doped BiFeO₃ Thin Film

At room temperature,bismuth ferrite（BiFeO₃）is the only single-phase multiferroic material（with ferroelectricity and G-type antiferromagnetic）.Over a long period of time,extensive research has been conducted on different forms of BiFeO₃ based materials,including ceramic sheets,nanostructures,and thin films.The interesting properties and versatility of BiFeO₃ thin films are enough,especially the great ferroelectricity,photovoltaic effect and inherent magnetoelectric coupling.Its excellent physical performance has made it widely used in phase shifters,ferroelectric random access memories,acoustic surface devices,and pyroelectric sensors.Then,BiFeO₃ thin films have inherent defects such as high oxygen vacancy concentration and leakage current density,which pose serious obstacles to their physical properties.The research content of this article mainly focuses on reducing defects,oxygen vacancy content,and leakage current density,and improving their physical properties.In this paper,BiFeO₃ thin films were prepared on FTO/glass substrates by sol-gel method.The main research results are as follows:This article mainly studies how to reduce defects,leakage current density,and oxygen vacancy concentration in BiFeO₃ thin films,thereby improving the physical properties of the films.In this paper,BiFeO₃ thin films were prepared on FTO/glass substrates by sol-gel method.The main research findings are as follows:（1）Firstly,Bi_1-xZr_xFeO₃ thin films doped with Zr at the A-site were prepared,and the effects of doping on the structure,microstructure,and physical properties of BFO thin films were studied and analyzed.Research has found that the Bi_1-xZr_xFeO₃thin film has a twisted rhombic perovskite structure,and the Bi_1-xZr_xFeO₃ thin film prepared in the experiment has no impurity phase.The SEM results indicate that the grain size of Bi_1-xZr_xFeO₃ thin film decreases,indicating a decrease in porosity.XPS data indicates that Zr⁴⁺can inhibit the generation of Fe²⁺and oxygen vacancies.Among them,the BFO film with a Zr⁴⁺doping amount of 2%has the lowest leakage current density(6.06×10^-7 A/cm²),3 orders of magnitude lower than pure BFO film.However,due to the doping of Zr⁴⁺,it may lead to a decrease in polarity R3c phase,resulting in a decrease in residual polarization intensity.In terms of optical performance,Zr⁴⁺doping changes the absorption coefficient and bandgap value of the thin film.（2）After studying the doping of tetravalent ions,the structure and properties of Bi_1-xLa_xFeO₃ thin films doped with trivalent ions(La³⁺)at the Bi site were studied.After La³⁺doping,the grain size of BiFeO₃ thin films decreased and particle clusters appeared.Due to the decrease in oxygen vacancy concentration,the leakage current density of La³⁺doped BiFeO₃ thin films will be as low as 1.1×10^-6A/cm²。The remaining plan value is effectively improved,and the remaining plan value of BLFO thin films with a doping amount of 2%reaches the maximum value（2P_r=280.4μC/cm²）。In terms of optical properties,La³⁺doping effectively reduces the band gap value of the thin film and widens the light absorption range.（3）Selecting Ca²⁺,Sr²⁺,and Mg²⁺ions as divalent doping ions to replace the Bi site,it was found that all three divalent ions reduce the grain size and have a significant impact on the bond length and quantity of Bi-O bonds,especially Sr and Mg ions.After single doping of three divalent ions,the transition from Fe³⁺to Fe²⁺is inhibited,and the oxygen vacancy concentration is effectively controlled.It is also shown that moderate doping of the three ions can significantly reduce the leakage current density.Among them,the lowest leakage current density of BFO thin films doped with Ca²⁺,Sr²⁺,and Mg²⁺ions is 2.17×10^-7 A/cm²、9.55×10^-8 A/cm² and1.56×10^-6 A/cm²,respectively.When the amount of Ca²⁺doped is 1%,the remaining planned value increases,but when the amount of Ca²⁺doped is further increased,the remaining planned value,like that of Sr and Mg doped,gradually decreases.This may be the decrease in the polarity R3c phase and the increase in grain boundary defects,which seriously hinders the amount reversal of ferroelectric domains.In terms of optical properties,three kinds of ion monodoping can improve the optical properties of the thin film to a certain extent.