Synthesis And Properties Investigation Of BiFeO₃ And Bi₂Mn₄O₁₀

BiFeO3 is one of the few known multiferroic materials having simultaneous ferroelectric and antiferromagnetic characteristics at room temperature, which has been regarded to be an excellent candidate for multiferroic applications.Meanwhile, the Bi2Mn4O10, displaying significant applications in catalysis and pigment, has attracted extensive attentions.Owing to the size effect and the surface effect, the nanoparticles have been reported to exhibit novel or enhanced properties, which are different from bulk samples.In this dissertation, BiFeO3 and Bi2Mn4O10 nanoparticles have been prepared and their properties were investigated systematically.The main points are summarized as follows:(1) A polyacrylamide gel route has been employed to prepare BiFeO3 nanoparticles.It was demonstrated that phase-pure BiFeO3 can be obtained using EDTA as the chelating agent. On the other hand, the size of BiFeO3 nanoparticles can be controlled by the addition of different ratio of N,N'-methylenebisacrylamide, and the size of particles decreased with increasing the content of N,N'-methylenebisacrylamide.Ferroelectric measurements proved that the BiFeO3 nanoparticles displayed ferroelectric property at room temperature.The magnetic measurements showed that the BiFeO3 nanoparticles exhibited weak ferromagnetism at room temperature,and the magnetization increased with decreasing the particle size. The ferromagnetism of BiFeO3 nanoparticles can be explained as the result of the suppression of spiral-modulated spin structure in the BiFeO3.Differential Scanning calorimerty analysis showed that the BiFeO3 nanoparticles had an antiferromagnetic phase transition at -370℃and a ferroelectric phase transition at -830℃. UV-vis diffuse reflectance spectrum investigation illuminated that the band gap of BiFeO3 nanoparticles was about 2.09eV.(2) The Bi2Mn4O10 nanoparticles have been synthesized by the polyacrylamide gel route.The XRD analysis showed that the products were phase-pure Bi2Mn4O10. The effects of experimental parameter on the morphology of the nanoparticles were investigated by SEM.The IR spectrum of Bi2Mn4O10 nanoparticles revealed several weak absorption peaks which can be attributed to the particle surface phonon modes. The magnetic measurements showed that the Bi2Mn4O10 nanoparticles exhibited weak magnetism at room temperature, which was quite different from the antiferromagnetism of Bi2Mn40io.The size effect in nanoparticles may be responsible for their magnetism.