【作者】 王芳；

【导师】 王金斌；

【作者基本信息】 湘潭大学 ， 材料科学与工程， 2014， 博士

【摘要】 铁电纳米材料具有优良的物理、化学性质，在高密度存储器、纳米发电机、纳米传感器、铁电隧道结、探针阵列等方面有着广阔的应用前景。而铁电纳米材料的奇特性能及应用与材料的形貌、尺寸有很大关系。因此，探索铁电纳米材料的可控制备条件及机理，对研究铁电纳米材料形貌与性能之间的关系具有重要意义，同时为铁电纳米材料应用领域的扩展提供可能性和依据。本文针对铋层状钙钛矿结构的Bi4Ti3O12铁电纳米材料结构复杂，可控制备困难的问题，利用水热/溶剂热法，探索和设计制备工艺路线，详细摸索了前驱体种类、矿化剂种类和浓度、表面活性剂、反应时间和温度等因素对Bi4Ti3O12纳米材料结构和形貌的影响。本论文的具体工作和相应结果如下：1、基于共沉淀前驱体Bi4Ti3O12纳米材料水热制备及性能表征采用共沉淀法制备水热前驱体，经过洗涤，去掉了前驱体中多余的离子，并系统研究了矿化剂种类和浓度、反应时间、反应温度对Bi4Ti3O12纳米材料结构形貌的影响。在一定的条件下，得到了由纳米片组成的Bi4Ti3O12空心球状结构，通过分析不同时间得到的产物，推断空心球的生长机制是Ostwald ripening。Bi4Ti3O12纳米片空心球的X射线光电子能谱结果显示纳米片表面有氧空位和吸附原子，并且由于表面缺陷能级引起紫外-可见光吸收发生红移。由透射电镜暗场像观察到纳米片具有5-50nm的纳米畴结构。由压电力显微镜(PFM)测试得到的压电回线和相图，结果表明Bi4Ti3O12纳米片有明显的铁电性，并且具有较高的压电系数(58pm/V)，这归因于纳米片的表面吸附引起的表面效应以及纳米畴结构的贡献。2、不同形貌的Bi4Ti3O12纳米结构的可控制备及性能表征通过氨水沉淀法分别制备了铋、钛前驱体沉淀，系统研究了该体系下矿化剂种类和浓度、反应时间对Bi4Ti3O12纳米材料结构和形貌的影响，得到了不同形貌的Bi4Ti3O12纳米材料：纳米片、薄片、纳米带、纳米棒。分析了该体系的水热反应机理，研究表明矿化剂有类似表面活性剂的作用，可以选择性吸附某些晶面，阻碍晶面生长，最终形成不同形貌的纳米材料。性能表征发现制备的Bi4Ti3O12纳米材料的紫外-可见光吸收峰略有红移，是由于Bi4Ti3O12纳米材料表面的缺陷能级引起的。由PFM测得的压电回线和相图可以看出Bi4Ti3O12纳米片和薄片有明显的铁电性。3、Bi4Ti3O12纳米材料的溶剂热制备及性能表征采用共沉淀前驱体体系和溶液前驱体体系，并探讨了溶剂种类和浓度、溶剂与水的比例(溶剂比)、反应时间、表面活性剂等因素对Bi4Ti3O12纳米材料结构和形貌的影响。得到了不同形貌的Bi4Ti3O12纳米材料：薄片、多级结构、纳米片。分析了溶剂热反应机理，通过调节表面活性剂的浓度，对微观结构和表面形貌的表征，发现阳离子表面活性剂的浓度对多级结构的生长和自组装过程起着至关重要的影响。4、不同形貌Bi4Ti3O12纳米材料的光电性能将以上水热/溶剂热法制备的Bi4Ti3O12纳米材料组装成染料敏化太阳能电池(DSSC)，进行了光电性能表征。结果表明Bi4Ti3O12纳米材料具有较高的光电活性，且纳米材料的形貌特征如形状、尺寸、晶面等对光电活性有较大的影响。暴露{101}晶面的Bi4Ti3O12纳米片样品组装的DSSC得到的最高短路电流密度为5.02mA cm2。通过表面原子排布图分析{101}晶面显露的Ti-O-键形成长链极大的提高了光生电子空穴对的传输，同时，交替排列的(Bi2O2)2+层和(Bi2Ti3O10)2层有利于光生电子空穴对的分离。5、酸蒸汽水热法制备铁电纳米棒阵列采用一种酸蒸汽水热法，即在水热釜中，将铁电薄膜置于盐酸液面之上，通过加热使盐酸溶液挥发，与铁电薄膜反应，使其生长成各种纳米材料的一种方法。采用不同厚度和不同材料的铁电薄膜，通过调节盐酸溶液的浓度和反应时间得到了纳米棒阵列。其生长机理实质上是溶解-再结晶过程，并在浓度梯度的驱动下，生长成纳米棒状结构。后续的工作将在铁电纳米棒的表征和更规则的铁电纳米阵列的制备上做出努力。更多还原

【Abstract】 Ferroelectric nanostructures become a hot topic of materials science and technology due to their novel properties and potential applications for nanoscale devices, including memorizers, transducers, sensors, and energy-harvesting devices. In nanostructures, morphology details such as size, shape, and aggregation form have a significant effect on the properties. Therefore, the controlled synthesis of ferroelectric nanomaterials has long been important topics of determining their properties and applications.Bismuth titanate (Bi4Ti3O12) has attracted growing attention from researchers due to their great properties and widely applications. As far as we know, there is no systemic study on controllable synthesis and growth mechanism of Bi4Ti3O12nanostructures. Herein, we demonstrate the effects of the kinds of precursor, the types and concentration of mineralizer, the surfactant and the reaction temperature and time on the shapes and structures of Bi4Ti3O12samples. Various single-crystalline Bi4Ti3O12nanostructures have been controllably synthesized by tuning the reaction parameters. The formation mechanisms of Bi4Ti3O12with different shapes are also investigated. Moreover, Bi4Ti3O12nanostructures with different shape have been firstly applied in the dye-sensitized solar cells (DSSCs). The main contents andresults results have been presented as follows.1、Bi4Ti3O12nanostructures were synthesized by hydrothermal process based on coprecipitation precursorBi4Ti3O12nanoplates were synthesized through hydrothermal process based on coprecipitation precursor. The effects of the kinds and concentration of mineralizer, the reaction temperature and time on the shapes and structures of Bi4Ti3O12samples have been analyzed. The formation mechanisms of the obtained hollow microspheres constructed by single-crystalline Bi4Ti3O12nanoplates are proposed to be Ostwald ripening. The characterization results show the surface of Bi4Ti3O12hollow microspheres exist the oxygen vacancies and the surface absorption, which will directly impact the atomic polarization for surface atoms and red-shift behavior. Piezoresponse Force Microscopy (PFM) was applied to explore the ferroelectric properties of Bi4Ti3O12nanoplates. The measurement showed that apparent ferroelectric properties of Bi4Ti3O12nanoplates and an enhanced piezoelectric coefficient d*33(58pm/V) of Bi4Ti3O12nanoplates than that of the BIT bulk single crystal. The possible reasons for such a large piezoelectric coefficient were analyzed by surface effects and nanodomain structures.2、Various morphologies of Bi4Ti3O12nanostructures were synthesized by a modified hydrothermal methodA modified hydrothermal method was applied to synthesize Bi4Ti3O12nanostructures. Single-crystalline Bi4Ti3O12nanostructures with various morphologies including nanoplates, lamellas, nanobelts and nanorods have been controllably synthesized. The effects of the kinds and concentration of mineralizer, the reaction time on the shapes and structures of Bi4Ti3O12samples have been analyzed. The kinds of mineralizers and their concentrations play important roles on the structure and morphology of Bi4Ti3O12products. A possible growth mechanism has been proposed by time-dependent experiments. In addition, PFM was applied to confirme the ferroelectric properties of Bi4Ti3O12nanoplates. Local piezoresponse force measurements display a typical butterfly curve and180o phase transition, indicating good ferroelectric property of the Bi4Ti3O12nanoplates and lamellas. UV/Vis absorption spectra have shown that the as-synthesized Bi4Ti3O12samples have a slightly red-shift behavior.3、Bi4Ti3O12nano-and micro-structures were controlly synthesized by a solvothermal methodA solvothermal method was applied to synthesize Bi4Ti3O12nanostructures. The effects of the kinds of solvent, the proportion of solvent and water, the kinds of surfactant, the reaction time on the shapes and structures of Bi4Ti3O12samples have been analyzed. Novel hierarchical Bi4Ti3O12micro-cross spheres with a diameter of about5μm were obtained. The hierarchical Bi4Ti3O12micro-cross spheres are consisted of nano-sheets which assemble into a cross intercalated structure. Moreover, the morphological evolution process indicates that the type and concentration of surfactant can adjusted the shape of Bi4Ti3O12nanostructures and the cetyltrimethylammonium bromide is important in determining the self-assembling process of Bi4Ti3O12micro-cross spheres. In addition, UV/Vis absorption spectra show that the as-synthesized Bi4Ti3O12samples have a slightly red-shift behavior and exhibit different band gaps with different morphologies.4、Morphology effects of Bi4Ti3O12nanostructures on the photoelectrochemical properties The morphology-dependent photoelectrochemical properties of Bi4Ti3O12nanostructures including nanoplates, lamellas, nanobelts, nanorods, hollow microspheres and micro-cross spheres were studied by applying for dye-sensitized solar cells (DSSCs). The results showed that the crystal facets of the Bi4Ti3O12nanostructure play important roles in the photoelectrochemical properties. The Bi4Ti3O12nanoplates with exposed {101} facets possessed the highest short circuit current density of5.02mA cm-2, fill factor of0.66, photovoltaic efficiency of2.56%. It is explained that the Ti-O-Ti-O bond chains are greatly enhanced the transfers of the photogenerated electron-hole pairs. This study demonstrates that Bi4Ti3O12nanostructure is a promising candidate as a DSSC.5、Ferroelectric nanorod arrays synthesized by a new acid vapor hydrothermalA new growth approach, acid vapor hydrothermal was adopted to fabricate ferroelectric nanorod arrays. The effects of the thickness of ferroelectric thin fims with different kinds of ferroelectric materials, the concentration of hydrochloric acid and the reaction time on the shapes and structures of ferroelectric thin films have been analyzed. The formation mechanisms of ferroelectric nanorod arrays Bi4Ti3O12have been proposed.更多还原