Preparation Of The One-dimensional Perovskite Oxides Materials And Their Physical Properties

one-dimensional nanomaterials exhibit novel physical properties and play an important role in fundamental research as well as practical applications. In 1991, Lijima fabricated the CNT successfully. Much attention has been paid to the synthesis of one-dimensional materials, many materials such as nanowires, nanofibers, nanorods et al have been prepared sucessfully.The methods for the synthesis of one-dimensional materials involve physical and chemical methods mainly. Evaporation and milling are typical physical methods. Chemical methods invole"bottom-up"and"top-down". In recent years, top-down approaches such as photolithography, soft lithography, and electrospinning have been exploited to fabricate 1D ceramic nanostructures successfully. Among various top-down approaches, electrospinning appears to be the most straightforward and versatile technique for generating 1D nanostructures. Electrospinning has exhibited a strong ability to generate polymeric nanofibers in the past decade. Combined with calcination or carbonation, ceramic or other inorganic nanofibers could also be synthesized using the electrospinning technique. Rencently, various means combined with electrospinning were applied to produce 1Dfunctional composite nanomaterials. With these techniques, the obtained 1D composite nanomaterials show good structure, stability, and properties.In this dissertation , we describes the preparation of perovskite-type LaFeO₃,SrFeO_3-δ and LaCoO₃ micro- nanofibers by electrospinning with Sol-Gel process. The preparation condition and formation mechanism were discussed in detail. The magnetic properties and the effects of the nanostructure on it were studied. The main results were as follows:(1) Effects of several important electrospinning parameters on the nanostructure of the perovskite oxides micro- nanofibers. The investigated parameters include PVP concentration, viscosity, the distance between the anode and cathode and the voltage et al. The experimental results indicated that, the continuous nanofibers with smooth surface could be obtained at the concentration of 8 wt.% to 12 wt.%, and the corresponding viscosity is 320～680cp. The size of the fibers decreased with the increase of the viscosity and when the voltage increased, it showed a increasing trend under a fixed distance.(2) Synthesis of one-dimensional LaFeO₃ nanofibers by electrospinning . Firstly, we prepared the precursor solutions by keeping the lanthanum ferrite inorganic and the 10 wt.% PVP composition at the different volume ratio. The results revealed that the continuous precursor fibers with average diameter of 300nm could be obtained at the ratio of 1:2. The XRD,SEM and TEM results indicated that after annealed at 600℃, the average diameter reduced to 200nm and perovskite type LaFeO₃ nanofibers with polycrystalline structure formed.(3) Synthesis of one-dimensional LaCoO₃ nanofibers by electrospinning . The LaCoO₃/PVP precursor fibers with average diameter of 400nm were obtained by the same electrospinning conditions. The XRD and TEM results showed that after annealing at 700℃, the LaCoO₃ nanofibers formed with a necklace-like structure, and the average diameter reduced to 300nm. Further more, TEM and ED images indicated its polycrystalline structure.(4) Synthesis and magnetic properties of one-dimensional SrFeO_3-δ nanofibers by electrospinning. The SrFeO_3-δ/PVP composite nanofibers were prepared by the same method above. These precursor fibers were annealed at different temperature. The SEM and XRD results revealed the SrFeO_3-δ/PVP composite fibers changed from continuous fibrous structure to a necklace-like structure following by the decomposition of PVP organic components and the chemical reaction of the inorganic salts. After annealing at 800℃, the one-dimensional SrFeO_3-δ nanofibers formed with a perfect polycrystalline structure and the average diameter was about 220nm. Finally, better magnetic properties were carried out by SQUID.