Fabrication Of ABO₃ Perovskite-type Oxide Micro/nanofibers Via Electrospinning

Nanostructure materials can be classified into zero dimensional (0D), one dimensional (1D), and two dimensional (2D) structural materials in the light of the definition of nanomaterial. These basic nanostructures become the small units for assembling the nanoscale building. Among the three nanostructures, 0D and 2D nanostructure are researched more early. The attention to 1D nanostructures start from 1991, since Iijima who comes from Japanese NEC Company found out carbon nanotubes the preparation and exploitation to quasi one dimensional or one dimensional nanostructures have been paid much attention. Subsequently, large numbers of methods in preparing variety one dimensional nanostructures emerged continuously. Among variety methods for preparing one dimensional nanomaterials, electrospinning is a simple but versatile process to fabricate one dimensional micro-/nanomaterilals. Compared with one dimensional nanomaterials prepared other processes, one dimensional micro-/nanomaterials fabricated using electrospinning are macroscale long in one-dimensional direction. In addition, large-scale production can be obtained using this process.Sol-Gel process has an important position in the preparation of nanostructure materials. Sol-Gel process has been widely used in the preparation of zero dimensional sol nanoparticles, one dimensional ceramic nanowire, two dimensional nanomembranes, and in the coating of nanomanterials. It will be significant to extend the applications of electrospinning technique and Sol-Gel process to incorporate them together to prepare novel one dimensional nanomaterial.With the rapidly development of nanometer science and technology, the electrospinning technique to be know again by the people of the world, and mainly used for fabrication the organic and biological materials micro-/nanometer fibers. In 2002, Prof. Kim and Prof. Shao et al. from the Chonbuk National University and the Northeast Normal University were first obtained the SiO2 nanofibers succeeded by electrospinning with the Sol-Gel technique. Since then, more than 20 varieties of ceramic fibers have been produced by this method.ABO3 perovskite-type complex oxides possess abundant physical and chemical properties, such as ferromagnetism, ferroelectricity, piezoelectricity, thermoelectricity, superconductivity, fluorescence, catalyst and colossal magnetoresistance etc, so they have important application as functional materials. With the increasing interests of superconductivity and colossal magnetoresistance (CMR) since the 1990's, the perovskite oxides become more and more attracting to the scientists. Several years recently, a series of research about ABO3 perovskite oxide nanomaterials had been investigated, however, limit to the preparation methods, mainly concentrates on the preparation and investigation of the 0D and 2D nanomaterials, it has few article about the quasi-one dimensional (1D) nanostructure ABO3 perovskite nanomaterials.This dissertation describes the preparation of the ABO3 perovskite oxides micro- nanofibers by electrospinning with Sol-Gel process, a series of the ABO3 perovskite structure micro-/nanofibers had been obtained successfully for the first time, and discussed its preparation condition and mechanism. We got the organic nanotube and ceramic nanotube through the coaxial electrospining technique, and conducted the preliminary study and the exploration; the main results were as follows:(1) Fabrication of the LaMnO3 nanofibers. Take the polyvinyl alcohol (PVA) as the complexing agent, prepares the PVA/LaMnO3 precursors, the diameter of the precursors fibers between 100 ~ 200 nm with smooth surface after electrospinning process. The diameter of the fibers thinning and the surface changes rough gradually after sintered at 400℃and 600℃for 2 h and 1 h, then the cubic polycrystalline structure LaMnO3 nanofibers were obtained with diameter between 50 ~ 100 nm. In the calcinations process, the crystal constant reduces unceasingly, it no longer change after sintered at 600℃, we thought this creates by the surface effect of the nanomaterials. Continues to enhance the calcinations temperature, the crystal grain of the nanofibers grows up unceasingly, then became the nanometer chaining, turns the micro-nanometer finely ground particles finally. The investigation of the TG-DSC, XRD and FT-IR indicate that the precursor fibers dehydrated process started at 122℃and end at 260℃. The formation of the La2O2CO3 andγ-Mn2O3 (the decomposition of PVA and the crystal of LaMnO3 starts to form also synchronize) mainly from 260℃to 360℃. The solid state reaction between La2O3 from the decomposition of La2O2CO3 andγ-Mn2O3 go along, this process will complete at 550℃with the pure LaMnO3 was obtained.(2) Fabrication of the SrTiO3 ultrafine fibers. Take PVP as the complexing agent, preparation of the precursors, and the diameter of the precursor's fibers between 100 nm ~ 1000 nm and the typical diameter was 700 nm after electrospinning process. We obtained the cubic SrTiO3 micro-nanofibers after sintered at 600℃, 800℃and 900℃for 2 h, 1 h and 1 h. The diameter of the ultrafine fibers between 50 nm ~ 400 nm, the typical diameter is approximately 280 nm. The average grains diameter of the constitution fibers is approximately 30 nm after calcites at 900℃. The investigation of TG-DSC, XRD indicated that the gathers thing-Ti(O-nC4H9) 4-x(CH3 COOH) x(x>2)has formed in the experimental system of Ti(O-nC4H9)4-H2O-CH3COOH. Between the electrospinning process, the solvent member and excessive water classification is traversing the network architecture separates out and volatilizes, and the strontium ion or acetate ion keep in the gelatin main body. Along with the increasing of calcinations temperature, the condensation responded continues to carry on, until decomposes produces TiO2, SrCO3, and further responded produces SrTiO3.(3) Fabrication of the La0.7Sr0.3MnO3 nanofibers. The diameter of the precursor fibers between 100 nm ~ 300 nm with smooth surface. The diameter of the fibers turn to 50 nm ~ 150 nm after calcine at 400℃and 600℃for 2 h and 1 h. The average grain diameter is 11.3 nm of the polycrystalline nanofibers. The EDS spectrogram indicated that Sr mixes in according to the corresponding proportion to LaMnO3, namely the sample is a La0.7Sr0.3MnO3 nanofibers. The investigation of TG-DSC, XRD, and FT-IR indicate that the formation of La0.7Sr0.3MnO3 nanofibers mainly has following several stages: First, the plural gel fibers takes off the ethanoic acid which in the absorbed water and the experiment completely responded to the decomposition reaction; Second, the crystal water takes off from the reactant and decomposition, simultaneously the remaining ethanoic acid continues to decompose; Third, the PVP decomposition, simultaneously continues take off crystal water; Fourth, the decomposition of the acetate ion of the compound; Finally, mainly decomposition of the CO32- in the La2(CO3)3, MnCO3 and the SrCO3, simultaneously crystallizes the response to start, the rhombohedral structure La0.7Sr0.3MnO3 nanofibers were obtained when the temperature achieved 580℃.(4) Fabrication of the La0.7Ca0.3MnO3 ultrafine fibers. The typical diameter of the PVP/La0.7Ca0.3MnO3 precursor fibers is approximately 1000 nm. We obtained the typical diameter about 800 nm of the orthorhombic structure La0.7Ca0.3MnO3 ultrafine fibers after calcines at 700℃. The ultrafine fibers is composed of the small crystal grains, which size is between 20 ~ 30nm. The result of TG-DSC and XRD indicated that the formation of La0.7Ca0.3MnO3 ultrafine fibers is similar to the La0.7Sr0.3MnO3 nanofibers, mainly has four stages: (a) escapes the absorbed water and the response ethanoic acid decomposition reaction; (b) escapes the crystal water, the PVP decomposition and so on; (c) compound acetate decomposition as well as PVP further decomposition burning; (d) forms middle metal carbonate decomposition, as well as La0.7Ca0.3MnO3 crystallization formation.(5) Fabrication of the polystyrene (PS) nanotube successfully utilizing coaxial electrospinning technique, and has carried on the preliminary exploration which a ceramic nanotube control prepares, obtained one kind ofα-La2O3 primarily, few SrCO3 is a mixed ceramic nanotube.The nanostructure controllable preparation and the application in electronics is the hot spot on the current international micro-nanosystematic research. Through preparation size, appearance and structure all controllable micro-nanostructure unit, then research assembly member electronic device, nanostructure sensor and the new component etc. Therefore, the preparation of one dimensional and quasi one dimensional ABO3 perovskite-type oxide ultrafine fibers, will be accepting domain electronics research for the extremely important application prospect. We apply the electrospinning with the Sol-Gel technique prepare the ABO3 perovskite-type oxides micro-/nanofibers, provide a simple and general method for prepared this kind of material. It is a preparation method and the research direction with development potential extremely. Simultaneously, the high surface areas of the electrospun fibers have the latent application value on catalysis. The key of this research field will be able to concentrate on the performance test and the applied research of this kind of electrospinning ultrafine fibers, as well as how can we use this kind of ultrafine fibers construction micro/nanoelectronic device in the future, will bring the recent development direction in nanometer science and technology.