With the rapid development of science and technology, multiferroic materials have become a research focus in the fields of sensors, microwave devices, data storage, spintronics, solar cells and so forth, exhibiting considerable application potential in intelligent materials and devices. The discovery of BiFeO3 and its derivatives, like Bi1-xAxFeO3 (A=La, Nd, Sm) and BiFexB1-xO3 (B=Ni, Mn, Co), has greatly accele-rated the advance of the multiferroic materials. This kind of material belongs to the single-phase perovskite type multiferroic materials, showing its superiority in integrated effects of ferroelectric, piezoelectric, dielectric, electrooptic, ferromagnetic, photovoltaic, magnetoelectric coupling and photocatalytic properties over room temperature. As a single phase multiferroic material, BiFeO3 features higher Curie temperature and Neal temperature, smaller optical band gap and better chemical stability compared with similar ferroelectric material. However, in the process of preparing BiFeO3, partial Fe3+ is converted to Fe2+, and bismuth is likely to volatilize because of its low melting point, producing a large number of oxygen vacancies and resulting in large leakage current. It is very difficult to have high residual polarization samples. Besides, weak magnetic properties of the BFO films at room temperature greatly limit its practical application. Over the years, scholars at home and abroad have devoted themselves to improving the preparation conditions and parameters, developing more advanced preparation methods, selecting more suitable substrate materials, preparing multilayer composite films and conducting ion doping et al. Among all the improvement approaches, ion doping plays the most prominent role to reduce leakage current, improve ferroelectricity and room temperature magnetism. Researchers over the world have successively prepared doped and composite BiFeO3 materials with superior properties to pure BiFeO3. Doping multiple elements at different positions rather than doping single element exert more favorable effect on improving the performance of BiFeO3materials. The residual polarization of Bi0.88Sr0.03Gd0.09Fe0.94Mn0.04Co0. 02O3 films with mixed doped ions prepared by sol-gel method has been raised to 108 μC/cm2, which is significantly higher than that of materials singly doped by La, Mn, Zn and other elements (69.47 μC/cm2). Meanwhile, the magnetization of the doped BiFeO3 film is three to four times higher than that of the pure BiFeO3 film. This may be derived from the inhibition of Bi3+ volatilization and Fe3+ reduction by doping elements, which contribute to reducing the oxygen vacancy and defect concentration, controlling the leakage current and raising the dielectric constant, and further improving the ferroelectric properties of the BiFeO3 film. In addition, doping elements also lead to the structural distortion and break the spiral magnetic structure of the material, thus producing strong magnetic properties at room temperature. Firstly, the structure of BiFeO3 materials and the types of doped elements in its modification are briefly described in this article. Secondly, the effects of A, B and AB co-doped ions on improving weak magnetic properties of BiFeO3 thin films and improving ferroelectric properties by redu-cing leakage current are discussed, and the reasons for the influences are further summarized. Finally, the research work to be carried out is proposed. © 2019, Materials Review Magazine. All right reserved.
