【作者】 张祖伟；

【导师】 胡陈果；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2008， 硕士

【摘要】 铈作为一种重要的稀土元素,在地壳中含量十分丰富,而氧化铈(CeO2)是一种廉价而用途极广的材料,广泛应用于发光材料、紫外吸收材料、催化剂、玻璃的抛光、耐辐射玻璃、电子陶瓷等领域。近年来,随着稀土新材料和纳米技术的迅速发展,人们发现纳米CeO2粉末具有新的优异性能及应用,CeO2纳米材料的制备、功能特性及应用研究己成为一个迫切需要研究的课题。本文采用一种低温常压、操作简单、成本低廉、便于工业化推广的合成新方法—复合氢氧化物媒介法(composite-hydroxide-mediated,CHM)合成出超细的纳米CeO2颗粒、纳米CeO2颗粒包覆碳纳米管以及钡掺杂CeO2纳米线。用CHM法合成的CeO2纳米颗粒通过XRD、TEM、HRTEM以及UV-vis的表征,发现其颗粒径很小,约2-8nm,用CHM法合成的CeO2纳米颗粒通过XRD、TEM、HRTEM以及UV-vis的表征,发现其颗粒径很小,约2-8nm,颗粒的对应晶面自组装组合。而导致了反常的XRD现象。利用CHM法在经过硝酸处理的碳纳米管上沉积了CeO2纳米颗粒,并对其进行了XRD、SEM、UV-vis和FTIR表征。发现纯碳纳米管表面具有很稳定的石墨结构,很难沉积CeO2纳米颗粒。但是碳纳米管经过硝酸处理之后,表面部分碳-碳双键被打开并上了羧基、羟基等官能团,而这些官能团可以作为活性中心而使CeO2纳米颗粒在其表面沉积并生长。因此碳纳米管的表面修饰是CeO2纳米颗粒能否沉积和沉积质量好坏的关键。通过CHM法对CeO2进行钡掺杂后,合成了一种新的纳米材料—钡掺杂的氧化铈纳米线。通过XRD、SEM、TEM和HRTEM的表征,发现它具有CeO2的萤石结构,独特的一维线状形貌,长3-20μm,纳米线结晶好为单晶,沿[110]方向生长,生长机理则遵从“溶解—结晶”模型。利用该纳米线做成的膜电极具有很好的湿敏特性,电极电阻随湿度变化剧烈,响应时间和回复时间分别为1分钟和2分钟。用离子导电模型解释了该电极的湿敏机理。通过光刻与聚焦离子束的方法搭建了单根钡掺杂CeO2纳米线电极并进行了伏安测试,单根纳米线的I—V曲线表现出轻微的非线性,我们用金属—半导体的表面接触效应对其进行了解释。更多还原

【Abstract】 Cerium is an important rare earth metal, and is richly contained in the earth. Ceria is a cheap and widely used material, which has been applied in the areas of luminous material, UV absorption material, catalyst, polishing, election ceramics, and so on. Recent years, with the development of nanotechnology and new rare earth materials, it is found that nano ceria powder have some novel properties and applications. So the research of synthesize, functional properties and application of nano ceria materials is an interesting subject.In this study, we developed a novel simple method composite-hydroxide-mediated (CHM) route to synthesize ceria nanoparticles, carbon nanotubes coated with ceria nanoparticles and Ba doped ceria nanowire. This method only requires low synthesis temperature and pressure, which is beneficial for mass-production with low costs.The ceria nanoparticles synthesized though CHM method are characterized by XRD, TEM, HRTEM and UV-vis analysis. The diameter of the nanopaticles is found to be very small, about 2-8 nm. We discover strong agglomeration of the nanoparticles, which induce the abnormal XRD pattern.The carbon nanotubes pretreated by nitric acid are coated with ceria nanoparticles. The products are characterized by XRD, SEM, UV-vis and FTIR analysis. We find that carbon nanotubes of perfect graphite structure can be hardly deposited with ceria nanoparticles. But when carbon nanotubes are pretreated by nitric acid, the graphite structure is partially destroyed with connecting hydroxyl and carboxyl on their surface. These functional groups work as active centers and make ceria nanoparticles deposit on the carbon nanotubes. So the surface modification of carbon nanotubes is very important for the coating of carbon nanotubes by ceria nanoparticles.Ba-doped ceria nanowires are synthesized by CHM method. Characterized by XRD, SEM, TEM, and HRTEM, the nanowires are found to have the typical fluorite structure, single crystal, and the length of 3-20μm. The growth direction of the nanowies is [110], and a‘dissolution- crystallization’model is proposed to explain the growth mechanism. The film electrode composed with Ba-doped ceria nanowires has an excellent humidity property, the resistance change sharply with the humidity. The response time and recover time of the humidity sensor are found to be 1 minute and 2 minute, respectively. The mechanism of humidity sensitivity is explained by the ion conductance model.The Ba-doped nanowire as building block contrusts a single nanowire FET with the help of Focused Ion Beam technology. The I-V curve of a single Ba-doped ceria nanowire is measured. The I-V curve is found to have a nonlinear behavior, which is explained by the metal- semiconductor contacting effect.更多还原