【作者】 王娟；

【导师】 韩高荣； 张溪文；

【作者基本信息】 浙江大学 ， 材料学， 2014， 博士

【摘要】 近年来,一维纳米多元氧化物材料以其新颖的微观结构(如纳米纤维、纳米管、纳米棒和纳米带)、不同于传统块材的特殊的物理和化学性能,以及在基础研究和微纳米器件应用方面的重要价值而受到人们的广泛关注。锆钛酸铅(PZT)作为一种铁电、压电性能优异的功能性材料,具有高机电耦合系数、大剩余极化强度、高介电常数、热电效应和高的光电系数等,在传感器、制动器、结构系统、非挥发性铁电存储设备、微机电系统(MEMS)等技术领域显示出十分重要的现实应用价值。而尖晶石相NiFe2O4铁氧体作为一种软磁材料,具有低的矫顽力、低涡流损耗和高的化学稳定性,在高密度磁记录、磁传感器、微纳功能器件、自旋电子器件等方面有望得到实际应用。制备一维微/纳米结构材料的方法多种多样,包括模板法、水热合成法、高分子辅助共沉淀法、磁场辅助自组装法和高压静电纺丝技术。在众多的方法中,高压静电纺丝技术具有制备过程简单、成本低廉、样式多变、可大量生产等优势,更重要的是较容易实现纤维的直径可控、形貌多样化,制备的纤维直径从几十纳米到数百纳米、长度达到宏观尺度。通过使用适当的收集器,还能够实现纤维的定向排列。本论文以高压静电纺丝技术为基础,与溶胶-凝胶技术和热处理工艺调控相结合,以铁电性材料锆钛酸铅和铁磁性材料铁酸镍为研究对象,实现了一维纳米纤维/纳米管的直径可控、形貌与相关性能的调控,主要工作和创新成果如下：1、采用静电纺丝技术制备了PVDF纤维结构,讨论了前驱体溶液的物理参数(溶液的浓度/粘度、溶剂比)和静电纺丝过程参数(施加电压、溶液流速和接收距离)等条件对所得纤维形貌和直径分布的影响,实现了PVDF纤维的直径从200nm到1.6μm可调。2、以静电纺丝法结合溶胶-凝胶技术和烧结工艺,成功制备了直径可控、成分在准同型相界附近、具有类单晶结构的PbZr0.52Ti0.48O3纳米纤维。调节前驱体溶液的物理参数(溶液的浓度/粘度)和静电纺丝过程参数(施加电压、溶液流速和接收距离),实现了PZT纳米纤维直径从50nm到540nm可调；烧结工艺(烧结温度、保温时间和升温速率)对PZT纳米纤维的形貌和相成分有显著的影响；引入分级退火制度,在400℃预烧结0.5h后,再在650℃烧结2h能够得到单一钙钛矿相的类单晶结构PZT纳米纤维,并研究了其形成机理。3、以同轴静电纺丝法结合溶胶-凝胶技术和烧结工艺,成功制备了直径可控、成分在准同型相界附近、具有类单晶结构的PZT纳米管。研究发现调节内、外层溶液的物理参数(溶液的浓度／粘度、PZT摩尔浓度)和静电纺丝过程参数(施加电压,内、外层溶液流速)能够调节凝胶纤维的直径,进而调节烧结后PZT纳米管的直径和壁厚,实现了PZT纳米管的外部直径从100nm到1.3μm可调,壁厚从50nm到～200nm可调。引入分级退火制度,在360℃预烧结0.5h再在700℃烧结2h后成功制得单一钙钛矿相的具有类单晶结构的PZT纳米管。4、以静电纺丝法结合溶胶-凝胶技术和烧结工艺,通过在不同的温度烧结,成功制备了直径约90nm的多颗粒纳米链和单颗粒纳米链NiFe2O4纳米纤维。发现烧结温度对NiFe2O4纳米纤维的形貌及其磁性能有显著的影响,单晶纳米颗粒组成的NiFe2O4纳米纤维的磁性能最优,室温下其饱和极化强度和矫顽力都比多颗粒纳米链高。这为研究NiFe2O4纳米链的尺寸效应和准一维纳米结构的磁化反转机理提供了较好的研究对象。更多还原

【Abstract】 In recent years, one dimensional (1D) functional nanomaterials with various morphologies, have attracted much increased attention due to their large specific surface area, high aspect ratio and unique shape anisotropy. Considering their distinctive physical and chemical properties from their bulk and nanoparticle counterpartes,1D nanomaterials can be used in various potential applications. Lead zirconate titanate (PZT) is widely used as ferroelectric materials in sensor, actuators, non-volatile ferroelectric memory devices, micro-electromechanical systems (MEMS), because of its highest electromechanical coupling coefficient, large remnant polarization, and high dielectric, pyroelectric, and electro-optic coefficients.1D PZT nano structures are expected to have more attractive properties than those of their bulk counterparts due to their reduced sizes and large surface-to-volume ratios, and fibrous PZT has great potential for utilization in high performance hydrophones and ultrasonic transducer applications. Recently, nanoscale spinel ferrites have also attracted much attention due to their unique magnetic and electrical properties. Since nickel ferrite has the low coercivity, low eddy current loss, and chemical stability, its diverse potential applications include high-density magnetic recording, magnetic sensor, micro/nano devices, spin-electron device, etc.In the last decade, many synthesis methods, including template preparation, hydrothermal routs, polymer-assisted co-precipitation method, magnetic-field-induced assembly and electrospinning process have been developed to fabricate ID micro/nanomaterials. Among these methods, electrospinning technique is a simple, low cost, versatile and effective technology for fabricating nanofibers in large scale. It has been utilized to synthesize size-controlled1D nanostructural material with various morphologies and the diameter ranging from tens to hundreds of nanometers. By virtue of the collection facilities to align fibers uniaxial, electrospinning has also been considered as a promising way to assemble ordered magnetic circuits instead of using expensive electron-beam lithography.In this dissertation, we combined electrospinning technique with sol-gel method and heat treatment process to synthesis size-controlled, morphology tunable1D nanostructures. The relevant characterization and property investigation of1D nano structures for ferroelectric PZT and ferromagnetic NiFe2O4materials have also been carried out. The main work and innovative results are as follows:1. Size-tunable piezoelectric polymer PVDF nanofibers have been fabricated via electrospinning technique. We discussed the influences of the precursor solution’s physical parameters (solution concentration/viscosity and solvent ratio) and electrospinning process parameters (voltage, flow rate, collect distance) on the fiber morphology and diameter distribution, and realized the PVDF fiber diameter tuned from200nm to1.6μm.2. Size-controlled single-crystal-like lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) ceramic nanofibers have been successfully prepared by sol-gel based electrospinning and subsequent calcination process. The fiber diameter can be precisely controlled from～50to540nm by varying the PVP concentration and electrospinning process parameters. The crystal structure of the nanofibers pyrolyzed at400℃for0.5h and calcined at650℃for2h is proved to be single-crystal-like tetragonal perovskite phase. A formation mechanism is also discussed based on the thermal decomposition process, effect of the calcination and pyrolysis procedure. It is found that the pyrolysis procedure is a critical factor for the fabrication of single-crystal-like structure PZT nanofibers using electrospinning.3. Size-controlled single-crystal-like lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) ceramic nanotubes have been successfully prepared by sol-gel based co-axial electrospinning and subsequent calcination process. We discussed the influences of the inner and outer solutions’physical parameters (solution concentration/viscosity and molar concentration) and electrospinning process parameters (inner/outer flow rate ratio) on the fiber morphology, diameter and wall thickness. The outer diameter of PZT nanotubes can be tuned from100nm to1.3μm and their wall thickness is varied from～50to200nm. After pyrolyzed at400℃for0.5h and calcined at650℃for2h, the obtained PZT nanotubes are tetragonal perovskite phase and single-crystal-like.4. We report a facile way to fabricate NiFe2O4multiparticle-chain to single-particle chain via sol-gel-based electrospinning and calcination. NiFe2O4nanofibers with tunable morphology can be obtained by virtue of different calcination temperature. The NiFe2O4single-particle-chain nanofibers exhibit the highest saturated magnetization (Ms) and coercivity (Hc) at room temperature compared to multiparticle-chain. This provides a unique model system for the fundamental investigation into the size-dependent magnetism of NiFe2O4nanofibers from multiparticle-chain to singleparticle-chain, and the magnetization reversal mechanism with the quasi-1D nanostructure.更多还原