纳米氧化铁的磁学性能及其电化学性能的研究

发布时间：2018-05-14 01:25

本文选题：氧化铁 + 纳米环　；参考：《宁波大学》2015年硕士论文

【摘要】：氧化铁纳米材料吸引越来越多的研究目光,主要是由于其在广泛且重要的应用。纳米氧化铁的各种性能与氧化铁纳米结构的形貌有着重要的联系。本论文中,选取了两种重要的α-Fe2O3纳米结构作为研究对象。通过水热法合成了不同壁厚的α-Fe2O3单晶纳米环及纳米管,并利用综合物性测量系统对样品的磁学性能进行了研究。同时也对α-Fe2O3纳米环在高性能锂离子电池负极材料上的应用作了系统的研究。本文的主要研究成果如下:(1)我们通过水热法合成了单晶α-Fe2O3纳米环和纳米管。通过高分辨透射电子显微镜和选区电子衍射发现纳米环和纳米管的轴向方向平行于晶体c轴。磁性测量结果表明,单晶纳米环在210K处存在一个一级Morin相变,而单晶纳米管中没有观测这种相变。目前的实验结果表明,Morin相变对纳米结构的形状有很强烈地依赖性。Morin相变对纳米结构形状的依赖性可以通过垂直和平行于晶体的c轴的正与负的表面各向异性常数来解释。(2)我们测量了α-Fe2O3不同纳米结构的从室温到980K之间的磁学性能。首先在高真空(9.5×10-6 Torr)下通过920K之前的磁学性能的测量来确定不同纳米结构的热稳定性。实验结果发现,高温高真空下存在一个α-Fe2O3向Fe3O4的相变过程,而且这个转变过程受纳米结构形状的强烈影响。实验数据表明,这种相变主要发生在晶体(001)表面。由于纳米环和纳米管结构的高的热稳定性,我们可以准确的测量到它们的Néel温度。纳米环与纳米管的Néel温度随纳米环与管的壁厚的减小而下降,符合Néel温度的二维有限尺寸效应。(3)我们通过一种简单的两步法成功制备了α-Fe2O3@C纳米环。与纯α-Fe2O3电极材料相比,α-Fe2O3@C纳米环表现出更高的容量以及更好的充放电倍率性能。更重要的是,α-Fe2O3@C纳米环具有更好的循环性能(在1000 m Ag-1的电流下循环充放电160次后仍保有815 m Ahg-1的容量)。由于α-Fe2O3@C纳米环的独特结构及优异的电化学性能,α-Fe2O3@C纳米环可以作为高性能锂离子电池极有前途的一种负极材料。同时,也可以以这种环状结构作为前驱体合成其它高性能的Fe2O3基锂离子电池负极材料。
[Abstract]:Iron oxide nanomaterials attract more and more attention, mainly due to their wide and important applications. The properties of nanometer iron oxide are closely related to the morphology of iron oxide nanostructure. In this thesis, two important 伪-Fe _ 2O _ 3 nanostructures are selected as the research object. 伪 -Fe _ 2O _ 3 nanocrystalline rings and nanotubes with different wall thickness were synthesized by hydrothermal method. The magnetic properties of the samples were studied by a comprehensive physical property measurement system. At the same time, the application of 伪 -Fe _ 2O _ 3 nanocyclic in the anode material of high performance lithium ion battery has been systematically studied. The main results of this paper are as follows: (1) single crystal 伪 -Fe _ 2O _ 3 nanorings and nanotubes have been synthesized by hydrothermal method. By means of high resolution transmission electron microscopy and selected area electron diffraction, the axial direction of nanospheres and nanotubes was found to be parallel to the c axis of the crystal. The magnetic measurements show that there is a first-order Morin phase transition at 210K in the monocrystalline nanocrystalline ring, but no such phase transition is observed in the single crystal nanotubes. The present experimental results show that the Morin phase transition is strongly dependent on the shape of the nanostructure. The dependence of the Morin phase transition on the shape of the nanostructure can be obtained through the positive and negative surface anisotropy constants of perpendicular and c-axis parallel to the crystal. We have measured the magnetic properties of 伪 -Fe _ 2O _ 3 nanostructures from room temperature to 980K. Firstly, the thermal stability of different nanostructures was determined by measuring the magnetic properties before 920K at a high vacuum of 9.5 脳 10 ~ (-6) Torr. The experimental results show that there exists a phase transition process from 伪 -Fe _ 2O _ 3 to Fe3O4 at high temperature and high vacuum, and this transition process is strongly influenced by the shape of nanostructures. The experimental data show that the phase transition mainly occurs on the crystal surface. Due to the high thermal stability of nanorings and nanotubes, their N 茅 el temperatures can be accurately measured. The N 茅 el temperature of nanorings and nanotubes decreases with the decrease of the wall thickness of nanometers and nanotubes. The two-dimensional finite size effect of N 茅 el temperature is conformed to the N 茅 el temperature.) We have successfully prepared 伪 -Fe _ 2O _ 3C nanospheres by a simple two-step method. Compared with pure 伪 -Fe _ 2O _ 3 electrode material, 伪 -Fe _ 2O _ 3 @ C nanorings exhibit higher capacity and better charge-discharge performance. More importantly, 伪 -Fe _ 2O _ 3C nanospheres have better cycling performance (the capacity of 815m Ahg-1 is retained after 1000 m Ag-1 current recharge and discharge 160m). Because of the unique structure and excellent electrochemical performance of 伪 -Fe _ 2O _ 3 @ C nanospings, 伪 -Fe _ 2O _ 3 @ C nanorods can be used as a promising anode material for high performance lithium ion batteries. At the same time, the ring structure can also be used as precursor to synthesize other high performance Fe2O3 based lithium ion battery anode materials.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.811

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