【作者】 倪世兵；

【导师】 贺德衍；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2010， 博士

【摘要】 过渡族金属氧化物由于具有多种化合价形式和特殊的结构而在许多领域有广泛的应用。本论文以四氧化三铁和钒酸锌为研究对象,以探索他们作为绿色环保材料在微波吸收和在Li离子二次电池中的应用为目标,采用简单水热法合成了这两种材料,并对它们的结构和物性进行了比较系统的评价。研究内容和所获得的结果主要包括以下几个方面：1、发展了简单水热法制备了分散性好的单晶四氧化三铁纳米颗粒,实现了对其形貌和尺寸的控制,得到了盒状、盘状和微球四氧化三铁。2、测试了四氧化三铁纳米颗粒和石蜡混合样品的微波吸收性能,表现出良好的吸收特性。当匹配厚度为3 mm,四氧化三铁体积分数为30%时,在8.16 GHz处最大反射损失值为-21.2 dB。进一步研究发现,C包覆的四氧化三铁颗粒的吸收频带宽度明显增加。当匹配厚度为4 mm,C包覆的四氧化三铁颗粒体积分数为70%时,混合样品的反射损失显示了从2.5到18 GHz的宽频吸收。3、电化学测量表明,四氧化三铁纳米颗粒和微球电极具有明显的充放电平台。在0.1 mA cm-2的电流密度下纳米颗粒电极的首次充放电容量分别为960 mAhg-1和1146 mAh g-1,50次循环之后保持容量分别为101 mAh g-1和102mAhg-1,整个充放电过程的平均库仑效率为95.66%。微球电极在0.1 mAcm-2的电流密度下首次充放电容量分别为856 mAh g-1和1141 mAhg-1,50次循环之后保持容量分别为123 mAh g-1和126 mAh g-1,整个过程的平均库仑效率为95.95%。纳米颗粒和微球电极的充放电容量对电压的微分曲线(dQ/dV)显示了明显的氧化还原峰,峰的位置和充放电平台一致,证实了四氧化三铁电极的充放电过程对应着氧化还原反应8Li++Fe3O4 (?) 3Fe+4Li2O。4、用简单水热法制备了焦钒酸锌(Zn3(OH)2V2O7·nH2O)纳米带,首次发现了它在室温下具有铁磁性。通过改变实验条件得到了片状、花状形貌的焦钒酸锌。对焦钒酸锌纳米片进行热处理得到了钒酸锌颗粒。光致发光测量表明钒酸锌在500-700 nm范围有强的可见光发射,研究表明,发光中心来源于Zn空位。电化学测量表明,Zn3(VO4)2电极在0.15V附近具有稳定的放电平台,在Li离子二次电池中有潜在的应用。更多还原

【Abstract】 Transition metal oxides were widely used in different areas due to their multi-form of oxidation states as well as their special crystal structures. The main object of this paper is to develop simple methods for the synthesis of transition metal oxide magnetite (Fe3O4) and vanadium zinc oxide (Zn3(VO4)2) that will have potential applications in green and environmental-benign fields, to research the microwave absorption of Fe3O4 and its application in lithium ion batteries, and to investigate the application of Zn3(VO4)2 as electrode in lithium ion batteries. In this paper, we report simple methods to fabricate Fe3O4 and Zn3(VO4)2, and their structures and applications were investigated in detail.1. Well dispersed Fe3O4 single crystal nanoparticles were synthesized by a simple hydrothermal method. Box-like, plate-like morphology and micro-spheres were obtained via tuning the reaction conditions.2. Fe3O4 nanoparticles and paraffin composites are of good microwave absorption properties. When the matching thickness is 3 mm, the calculated reflection loss of the composite reaches a maximum value of-21.2 dB at 8.16 GHz with 30% volume fraction of Fe3O4. Wide region of microwave absorption is achieved for carbon coated Fe3O4. When the matching thickness is 4 mm, the calculated reflection loss of the composite with 70% volume fraction of carbon coated Fe3O4 exhibits broad microwave absorption ranges from 2.5 to 18 GHz.3. Electrochemical properties of Fe3O4 nanoparticles and microspheres as negative electrodes of lithium ion batteries were studied by conventional charge/discharge test, showing obvious charge/discharge platforms. For Fe3O4 nanoparticles electrode, the initial charge and discharge capacity at current density of 0.1 mA cm-2 arrived at 960 mAh g-1 and 1146 mAh g-1, respecitively. After 50th cycles, the charge and discharge capacity maintain at 101 mAh g-1 and 102 mAh g-1, respectively. The mean coulombic efficiency of Fe3O4 nanoparticles electrode during the charge/discharge test at current density of 0.1 mA cm-2 is 95.66%. For microsphere electrode, the initial charge and discharge capacity at current density of 0.1 mA cm-2 arrived at 856 mAh g-1 and 1141 mAh g-1, respectively, maintaining at 123 mAh g-1 and 126 mAh g-1 after 50 cycles. The mean coulombic efficiency of Fe3O4 microsphere electrode during the charge/discharge test at current density of 0.1 mA cm-2 is 95.95%. The differential charge/discharge capacity versus voltage curves of Fe3O4 nanoparticles and microspheres electrodes show obvious oxidation and reduction peaks that are in good accordance with charge/discharge platforms. It indicates a reaction between Fe3O4 and Li+during the charge and discharge process, which is likely to be 8Li++Fe3O4 (?) 3Fe+4Li2O.4. Zinc vanadium oxide hydroxide hydrate (Zn3(OH)2V2O7·nH2O) nanobelts were synthesized via a simple hydrothermal method. It is firstly found that the as-synthesized nanobelts are ferromagnetic at room temperature. By changing the reaction condictions, nanosheets and flower-like morphology were successfully synthesized. Zinc vanadium oxide particles were obtained via annealing Zn3(OH)2V2O7·nH2O nanosheets at air atmosphere. Photoluminescence measurement shows strong visible light emission ranges from 500 nm to 700 nm, and the green emission center was proved to come from Zn vacancies in Zn3(VO4)2. Electrochemical properties of Zn3(VO4)2 electrode were studied, which shows steady platforms near 0.15 V during the first discharge curves, endowing it with potential application in lithium ion battery.更多还原