Preparation In Sol-gel Method,Characterization And Application Of BiFeO₃ Film With Eu And Co Doping

With the characteristics of ferroelectricity, ferromagnetism, ferroelasticity and magnetoelectric coupling et al, multiferroic materials have been widely used in aspects such as the sensors, storage devices and magnetoelectric coupling devices. Among numerous multiferroic materials, BiFeO₃ becomes the most potential single-phase multiferroic materials by the advantage of Curie temperature?TC? and Neel temperature?TN? which are higher than the room temperature, thus becomes the research hotspot. Currently BiFeO₃ still exists four aspects of problems: a) The preparation of pure BiFeO₃ with good crystallization is very difficult; b) Large leakage current could easily penetrate material, so it's difficult to get the saturated intensity of polarization of material; c) We can't get good ferroelectricity and ferromagnetism at room temperature; d) Ferroelectric coupling is very small, and there's a quite far distance from the needed requirements of application.In this paper, we use the sol-gel method to dope and improve BiFeO₃ film, the doping effect is very good. The application of BiFeO₃ film has also been tried and we get quite good results: better hysteresis phenomenon, switch characteristics of symmetric structure model, phenomenon of unipolar resistance change and ratio of the resistance value which is close to the application.The main work in this paper includes:1. Prepare the pure-phase BiFeO₃ film by using sol-gel method, make structural characterization of the sample film, and test its ferroelectricity and ferromagnetism. The results show that the crystalline structure of the sample film grown on the Si substrate accords with the space point group R3 c, annealing 120 minutes, got the pure phase BiFeO₃ film with very good crystallization; The BiFeO₃ films grown on Cu/Ti/Si O2/Si substrates showed impurity phases, angular deviation and wider diffraction peak also occurred, which proves the film is affected by the stress of the substrate; The residual intensity of polarization is 2.03 ? C/cm2 in electric performance test at room temperature, but the electric hysteresis loop is not full, it may be caused by the large leakage current; The residual intensity of magnetization is 0.543 emu/cm3 in magnetic performance test, although the magnetic hysteresis loop is very narrow, and showed weak magnetism, the data has been higher than previously reported.2. Dope and improve the pure-phase BiFeO₃ film with A-position Eu and B-position Co, and make structural characterization and ferromagnetic tests of the sample films. The results show that the crystallization of A-position Eu doping is superior to B-position Co doping, and the crystallization of B-position Co doping is superior to the pure-phase film. The structural phase transition didn't happen via doping, and the crystallization of the film is better; Magnetic analysis: the residual intensity of magnetization of B-position Co doping increased by 22% than pure-phase film, the residual intensity of A-position Eu doping decreased 31% than pure-phase film, although A-position Eu doping weakened the magnetism of film, the saturation intensity of magnetization is 2.5 times higher than that of Z.Q.Hu et al by adopting this technology. Overall, the magnetism and quality of film can be effectively improved through doping.3. This paper prepares BiFeO₃ film into FTJ structure and makes exploration of its application in memristors. The test results show that: a) the bipolar test method can get switch characteristics with better hysteresis phenomenon and symmetric structural model; b) the unipolar test method can get the phenomenon of unipolar resistance change and the ratio of resistance value which is close to the application.