【作者】 冷静；

【导师】 许大鹏；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2010， 博士

【摘要】 一维纳米材料由于其独特的结构和新颖的物理、化学和生物学特性,在催化、传感、电子器件等方面有着很大的基础研究价值和潜在的应用价值。1991年日本Lijima等人对碳纳米管的发现为一维纳米结构的研究与应用开辟了崭新的方向,掀起了国际上对一维纳米材料的科研热潮。随着研究的不断深入,各种一维纳米材料,诸如:纳米管、纳米棒、纳米线和纳米纤维等被相继合成。一维纳米材料的制备方法主要分为物理方法和化学方法。物理方法主要有热蒸发法和物理粉碎法等;化学方法包括自下而上（bottom-up）和自上而下（top-down）两类。常见的化学方法有气液相生长、模板法、静电纺丝法、光化学蚀刻等。静电纺丝技术最初被用于有机高分子聚合物超细纤维的制备,近些年来,人们把这项技术与sol-gel技术结合,合成了几十种一维无机纳米材料,这些材料以氧化物纤维为主。与大多数方法相比,静电纺丝法被公认为是最简单有效的制备一维纳米材料的方法。随着电纺研究的不断深入,人们已经不再停留于对材料的形貌和结构的有效控制等方面的基础性工作,开始注重研究这些具有一维纳米结构材料的奇特的性能,各种功能性一维纳米材料被相继合成。另外,制备方式也不再拘泥于静电纺丝技术与sol-gel的结合,研究人员开始将静电纺丝技术与其他各种物理化学方法相结合,并合成了一系列复合纳米材料。钙钛矿型复合氧化物ABO₃具有稳定的晶体结构、独特的电磁性能以及很高的氧化还原、氢解、异构化、电催化等活性,在固体燃料电池、固体电解质、传感器、高温加热材料、固体电阻器及替代贵金属的氧化还原催化剂等诸多领域有着广阔的应用前景。目前,其相关研究多为纳米粉体或块体的制备,而有关钙钛矿型复合氧化物纤维制备的报道较少。本文利用静电纺丝法制备了多种具有钙钛矿型结构的氧化物微/纳米纤维,详细讨论了这些微纳米纤维的纳米结构控制条件和形成机制,并研究了纤维的电磁学性质及材料的微观纳米结构对性能的影响等,具体工作如下:（1）详细讨论了静电纺丝过程中几个重要的参数（浓度、粘度、电压及喷丝头与收集板之间的距离）对纤维的形成和最终形貌的影响。实验结果表明,前躯体溶液的PVP浓度控制在8～12wt%,溶液粘度在320～680cp,可以形成直径均匀、表面光滑、连续的一维纳米结构的纤维,纤维的直径随粘度的增加变小。当喷丝头与收集板间距固定在12cm,流速为0.1ml/h时,电压值控制在10～16Kv,电纺过程比较稳定,纤维的形成以喷丝头处液滴的劈裂为主,随着电压的增加,纤维直径减小。当电压值固定,纤维直径则随着喷丝头与收集板之间的距离的增加而减小。（2）利用静电纺丝法结合sol-gel技术制备合成了LaFeO₃纳米纤维。讨论了乙酸镧[La（OOCH₃）₃·1.5H₂O]和乙酰丙酮铁[C₁₅H₂₁FeO₆]的盐溶液与10wt%的聚乙烯吡咯烷酮（PVP）的乙醇溶液的体积比对复合纤维形貌的影响。SEM结果表明随着La和Fe的盐溶液与PVP溶液体积比的减小,前躯体混合液的粘度增加,纤维直径变小。体积比控制在1:2时,纺丝效果较好,获得了平均直径在300nm左右、表面光滑且长直连续的一维纳米纤维。以该比例下的纤维为研究对象,讨论了烧结温度对纤维形貌及晶体结构的影响。XRD、SEM及TEM结果表明,600℃烧结后形成了较好的具有正交晶系钙钛矿多晶结构的LaFeO₃纳米纤维,其平均直径为200nm。700℃烧结后,纤维断裂。温度达到800℃以上,纤维结构转变为颗粒。（3）制备了LaCoO₃纳米纤维。以10wt%的PVP溶液作为络合剂,按1:2体积比配制LaCoO₃/PVP前躯体凝胶进行电纺,获得了平均直径约为400nm的表面光滑且连续的复合纳米纤维。在不同温度下烧结后,SEM结果表明600℃下,样品形成多孔纤维结构,平均直径约为300nm;在700℃、800℃时,转变为项链状纤维结构,直径变化不明显;温度达到900℃以上时纤维结构破坏。XRD结果表明,LaCoO₃纳米纤维在700℃时成相。TEM结果及同心环状电子衍射图为进一步印证,LaCoO₃纳米纤维为多晶结构。（4）制备了SrFeO_<sub>3-δ纳米纤维并研究了其磁性能。以上述相同方法制备SrFeO_<sub>3-δ/PVP复合纤维,并分别在700℃、800℃、900℃和1000℃下煅烧。SEM结果表明,700℃烧结后,样品保持了连续的纤维状结构,但由于PVP、醋酸根等有机成分的分解,纤维的平均直径从原来的500nm减小为400nm。800℃烧结后,由于纤维中的SrFeO_<sub>3-δ进一步结晶反应,形成了表面粗糙、多孔的一维纳米结构。900℃下,纤维的形貌发生了明显的变化,形成了由尺寸均匀小晶粒串联而成的项链状纳米纤维结构。纤维的直径急剧减小为220nm。1000℃以上,纤维结构破坏,无法保持一维纳米结构。XRD、TEM及ED结果表明,800℃以上形成了多晶结构的立方钙钛矿型SrFeO_<sub>3-δ纳米纤维。900℃下样品的热磁曲线（ZFC-FC）表明纤维样品磁学性能优于块体样品,其奈尔温度相对于其他块体样品等明显升高,居里温度也相应的升高。更多还原

【Abstract】 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.更多还原