Study On Sol-gel Synthesis Of BiFeO₃Ceramics And Its Doping Modification

As a typical single-phase multiferroic material, ferrite bismuth (BiFeO3), with high ferroelectric Curie temperature Tc (-1103k) and antiferromagnetic Neil temperature TN (-647k), is one of the few ferromagnetic materials in which both ferroelectricity and antiferromagnetic order are shown at room temperature. Therefore, BiFeO3-based multiferroics are potential substitutions for PZT as the next generation of lead-free piezoelectric materials with strong application value because of well ferroelectric effect and ferroelectric phase transition temperature.The great leakage current and low dielectric constant caused by the Bi volatilization and the valence fluctuation of Fe is one of the greatest problem in BiFeO3prepared at present. Only by doping and the solution method can the problem be improved in the ceramics study. This subject prepared BiFeO3powders and ceramics by a wet chemical method-sol gel. Besides, the doping modification and effect of doping on its performance are studied.First, The BiFeO3powders were prepared by sol-gel method, the factors in the conditions of preparing BiFeO3were studied according to the phase, morphology, ferromagnetism and dielectric properties of BiFeO3. XRD shows that glycol and glacial acetic acid are good solvent choice in preparation of well BiFeO3precursor and pure phase BiFeO3by Sol-Gel method; DSC curves combined in the analysis presents that BiFeO3phase formed at above400℃and well perovskite crystal can be achieved at500℃;1-1.5h is advisable to get pure BiFeO3;3%excess of Bi was added to compensate for the volatilization loss of Bi in the annealing process. On the condition of550℃/1.5h/Bi-3%/ethylene glycol and glacial acetic, well morphology can be seem from the SEM results; Rare magnetism (Mr=4.86E-6emu/g)can be seen from the VSM result. Ceramics sintered at800℃for1.5h show well compactness with actual density98%of the theoretical density.Bi1_xNdxFeO3, Bi0.9Nd0.1Fe1-y Tiy03precursors were also prepared by sol gel method. Annealed at500℃/650℃respectively for1.5h, pure ferrite bismuth was achieved. Study on effect of different dopingelements and amount on the ferrite phase morphology, ferromagnetism, dielectric properties was conducted. It is found that the magnetization was enhanced significantly with increasing Nd3+content, being attributed to the suppress of the spiral colloidal magnetic structure led by the phase structure transition. The spontaneous magnetization (Ms) of BiFeO3is also greatly increased from 0.12emu/g to the maximum value of0.34emu/g for x=0.075. The introduction of Ti makes a important role in changing the size and shape of ferrite bismuth. Dielectric loss decreased one order of magnitude (less than0.02at high frequency), showing that the doping of Nd and Ti has great effects on the performance of the ferrite bismuth that lays a solid foundation for the further research.