【作者】 王志；

【导师】 唐晓东； 彭晖；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 铋系材料因铋的费米面各向异性倾向性较强、载流子浓度低并且运动速度快、电子有效质量非常小而自由程很长等特殊的电子结构及电子特性,其单质和化合物近年来在科学研究和工业应用中频频崭露头角。而材料的纳米化能使其展现出体材料无法企及的许多奇特的优越性能。纳米尺寸的铋系材料其物理特性不仅得到了极大的优化,并且伴随着一些新的物理现象的出现,使其成为当前研究的一个热点。本论文主要研究了微纳尺度单质铋和铁酸铋的化学制备方法及其结构、尺寸和形貌的调控手段,并研究了其对相关物理特性的影响,具体如下：1.发展了一种制备铋纳米球的简单方法,利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)研究了反应温度、时间、包覆剂和快速淬灭等因素对纳米球的结构、尺寸和形貌的影响。光谱性能研究发现,所制备的铋纳米球在可见光区存在一个驼状吸收峰和一个在近红外区1940nm处的吸收峰,并对其产生原因进行了分析。磁学特性研究表明,铋纳米球抗磁性随着其尺寸的减小而变小,这与理论计算指出的铋纳米球禁带宽度与抗磁性关系是一致的。光限幅效应实验指出其可用于开发光限幅器件。光催化降解罗丹明B实验表明铋纳米球在光催化降解环境污染物方面也有潜在应用。2.采用微波水热法制备得到纳米尺度的纯相BiFe03晶体,其反应时间要远小于传统的水热法。X射线衍射(XRD)和能量色散X射线谱(EDX)测试表明,随着微波加热时间的进一步延长,合成的纯相BiFeO3纳米晶体会经历一个生成、分解和再生成的循环过程,这可能是由于这种特殊的微波加热方式,导致反应体系中的BiFeO3晶体的局域温度达到了BiFeO3的分解温度。与此同时,样品的磁性分析发现,其磁性在微波加热过程中的变化与XRD结果吻合很好。3.采用微波水热法制备了微米级BiFeO3晶体,发展了一种超声纯化的方法对粗产物进行了有效提纯,并发现聚阴离子—聚(甲基乙烯基醚共聚马来酸)(PMVEMA)对微米级BiFeO3晶体形貌有着明显的调控作用——随着聚阴离子用量的增加,BiFeO3晶体形貌从微米级的球逐渐演变成微米级的立方体,并提出了一种引起这一形貌变化的可能形成机理。磁学研究表明聚阴离子对BiFeO3形貌的调控并没有对其磁性产生影响,原因在于晶体尺寸大于BiFeO3自旋磁矩螺旋排列的周期。4.通过在前驱体溶液中加入聚阴离子PMVEMA,实现了对所制备BiFeO3纳米颗粒形貌和晶粒尺寸的调控。实验证明聚阴离子的引入并没有导致其它杂相的产生。形貌分析发现,一定量的聚阴离子PMVEMA的引入能使BiFeO3形貌出现纳米片形状,随着PMVEMA用量的增加使BiFeO3纳米晶粒粒径变小。对其紫外可见光学吸收谱研究发现,BiFeO3纳米颗粒禁带宽度在聚阴离子调控下发生变化,这可能是由于其粒径的变化导致的。磁学性能的研究也证明了PMVEMA对BiFeO3形貌和晶粒的有效调控,样品的磁性能随着铁酸铋纳米晶粒粒径的减小而增强。更多还原

【Abstract】 For unique electronic structure of bismuth such as small electron effective-mass, low charge carrier density, and long mean free path, bismuth and its compounds have found great applications in fundamental research and industry. Nanomaterials exhibit many unique properties which are quite different from their bulk materials. Nanosize bimsuth and its compounds which can optimize the physical properties and result into new physical phenomena have attracted more and more attention.In this thesis, we successfully prepared bismuth and bismuth ferrite nanomaterials and investigated the effect of the size and morphologies on their physical properties. The main achievements are as follows:1. A facile thermolysis method was developed to prepare well-defined bismuth nanospheres. The effect of temperature, surfactant and quenching process on the size and morphologies of bismuth nanomaterials were investigated by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). A camel-like shapes located at425nm and575nm in visible range were revealed by UV-NIR spectrophotometer. A new peak located at1940nm in the infrared range was first reported. The diamagnetic magnetization decreases with the decrease of the size of the bismuth nanospheres The result is in accordance with the relationship between the bandgap and diamagnetic magnetization reported in the literature. The optical limiting effect experiment illustrated that it can be used to develop new optical limiting device. The photocatalytic experiment shows that the bismuth nanospheres can be used as a catalyst to degrade the pollutants.2. The highly pure phase nanocrystal BiFeO3was prepared by using the microwave assisted hydrothermal method. The preparation time is much shorter than that of the traditional hydrothermal methods. An interesting phenomenon was observed that BiFeO3with pure phase periodically appeared during the microwave heating process revealed by XRD. The investigation of the magnetic properties of prepared samples also revealed the periodical formation of the pure phase BiFeO3. The magnetization of the three pure phase BiFeO3samples increased as the heating time increased.3. The mirocrystal BiFeO3was also obtained by using a microwave assisted hydrothermal method. An ultrasonic purification method was developed to obtain pure phase BiFeO3from the crude products without using any chemicals and the X-ray diffraction (XRD) testified the effective of this purification method. The morphology of BiFeO3was successfully modulated from microsphere to microcube by using a polyanion poly (methyl vinyl ether-alt-maleic acid)(PMVEMA). With the amount of PMVEMA increasing, the morphology of BiFeO3gradually evolved from microsphere to microcube observed by using SEM. A formation mechanism is suggested to illustrate the morphology evolution of BiFeO3. The magnetic properties of these microcrystals almost unchanged because the crystal size was larger than the superimposing wavelength in the spiral spin arrangement of BiFeO3.4. The introduction of PMVEMA can affect the morphologies of BiFeO3nanocrystal. The XRD results revealed that the introduction of the polyanion PMVEMA did not result into the appearance of impurity phases. BiFeO3nanoplates can be obtained by introduction of a certain amount of PMVEMA and further increasing the amount of PMVEMA resulted into the finer BiFeO3nanocrystals. The magnetic and optical evolution of BiFeO3nanoparticles confirmed that their properties were changed with their size.更多还原