【作者】 邓兆；

【导师】 戴英；

【作者基本信息】 武汉理工大学 ， 材料物理与化学， 2010， 博士

【摘要】 铁电元器件的不断小型化、集成化、功能化对低维铁电材料的研究和应用提出了新的要求,制备新型一维铁电纳米材料并对其性能进行研究以揭示其铁电性能与尺度、维度以及组成的相关性具有重要的理论价值和现实意义。本文以BaO-TiO2体系为研究对象,采用熔融盐法、模板法制备BaTiO3、BaTi2O5等一维铁电纳米材料,对材料的制备、结构进行深入研究,并采用现代测试手段对所制备的单根一维铁电纳米材料进行了压电、铁电及漏电流性能的研究。论文主要研究内容如下：(1)采用熔融盐法制备高产率BaTi2O5单晶纳米线。制备出的BaTi2O5单晶纳米线矩形截面长80-200nm,宽70-150nm,纳米线长度为几微米到几十微米。系统研究起始源材料、熔盐种类、熔盐比例、温度、时间等对产物相组成和形态的影响规律,获得了制备高产率单晶BaTi2O5纳米线的最佳工艺条件。BaTi2O5纳米线的生长受晶体的各向异性主导,在生长不受限制的熔融盐条件下具有很强的各向异性生长趋势,生长成为一维纳米结构。同时,反应初期,伴随BaTi2O5相形成BaTiO3、Ba4Ti13O30相也存在,而且Ba4Ti13O30是一维形态。随着反应时间的延长,各物相间经过复杂的化学反应最终形成纯相的单晶BaTi2O5纳米线。(2)对目前尚存争议的熔融盐法制备BaTiO3纳米线的工艺进行研究,如表面活性剂、熔融盐种类、温度、保温时间等对产物相组成和形态的影响。研究表明,熔融盐法直接制备BaTiO3一维纳米材料有一定难度,此方法所得产物中存在的少量一维相可以被标定为：BaTi2O5,BaTi5O11,BaTi13O30,Ba6Ti17O40-x等物相,没有观察到一维BaTiO3存在。这说明,具有高对称性晶体结构的立方相BaTiO3不易在熔融盐环境中呈现各向异性生长,而BaTi2O5,BaTiO11, Ba4Ti13O30,Ba6Ti17O40-x等具有高非对称性结构的物相在熔融盐环境中易于沿着某一特定的方向取向生长。基于此,通过调整原料Ba/Ti比、控制工艺参数,制得了Ba4Ti13O30、BaTi5O11等一维纳米材料。该熔融盐法为制备BaO-TiO2体系一维纳米材料提供了一条新途径。(3)采用模板法制备一维BaTiO3纳米材料。提出通过熔融盐模板法制备单晶BaTiO3纳米线的新思路：以单晶BaTi2O5纳米线为模板,通过化学共沉淀法在其表面包覆一层草酸钡,再置于熔融盐中煅烧,成功制备出单晶BaTiO3纳米线。与直接于空气中煅烧前驱体得到的BaTiO3纳米线比较,熔融盐环境更有益于制得结晶完好的单晶BaTiO3纳米线。此外,以钛酸钾纤维为模板,采用水热法低温条件下经过离子交换成功制备了BaTiO3纤维。以水合钛纤维为模板,通过化学共沉淀法在其表面包覆一层草酸钡,再经过空气中煅烧也成功制备了BaTiO3纳米线。该类方法制备BaTiO3纳米线符合自牺牲模板引导的原位反应机理,其中化学共沉淀法对一维模板的包覆是关键因素。这种自牺牲模板引导的原位反应制备一维纳米材料的方法是制备复杂氧化物一维纳米材料的有效途径。(4)单根BaTiO3、BaTi2O5铁电纳米线性能的研究是一个全新的课题。采用SPM、铁电工作站和纳米操控平台等手段研究了单根BaTiO3,BaTi2O5纳米线的性能。原位压电性能测试表明,BaTi2O5纳米线具有较好的压电性能,实验测得其d33*值约为300pm/V,而BaTiO3纳米线的d33*值较低约为15pm/V。沿纳米线直径方向铁电性能测试表明,在相同电压下,BaTi2O5纳米线的Pr约为BaTiO3纳米线的10倍；而沿纳米线生长方向的铁电性能测试表明,BaTi2O5纳米线和BaTiO3纳米线的Pr在一个数量级。单根BaTi2O5纳米线漏电流研究表明,在低电压范围内,漏电流复合欧姆定律,在高电压范围内漏电流符合空间限制电流机制(SCLC)),其电导率约为2×10-6S/cm。更多还原

【Abstract】 As the ferroelectric devices are taken development on minimization, integration and functionalization, there is growing interest in preparing low-dimensional ferroelectric nanostructure materials. The preparing of new one-dimensional ferroelectric nanostructures and exploring the relationship between their ferroelectric property and the scale and dimension are of great importance for both of fundamental research and technical applications.In this dissertation, the BaO-TiO2 system materials were chosen as the object of study. One-dimensional nanomaterials such as BaTiO3 nanowires and BaTi2O5 nanowires were synthesized by molten salt synthesis method or templating method. The synthesis process and the structure of the materials were studied intensively. Moden testing methods were used to explore the properties of the individual ferroelectric one-dimensional materials, such as piezoelectric property, ferroelectric property and leakage current. The main contents of the dissertation are described as follows:(1) Single-crystalline BaTi2O5 nanowires have been successfully prepared by a molten salt synthesis rout in high yield. The as-synthesized BaTi2O5 nanowires have a uniform structure with rectangular cross section (about 80-200 nm in width,70-150 nm in thickness) and lengths reaching up to tens of micrometers. The effects of raw material, salt type, the ratio of mixed salts, annealing temperature and annealing time on the phase composition and morphology of the products have been discussed. The optimum process condition has been obtained. The growth of BaTi2O5 nanowires is resulted from the anisotropy of the crystal structure. In the molten salt environment, BaTi2O5 crystal was more easily to form a wire-like structure. BaTiO3, Ba4Ti13O30 were formed together with BaTi2O5 phases at the beginning of the synthesis. And Ba4Ti13O30 was in a one-dimensional structure. With the annealing time prolong, pure phase BaTi2O5 nanowires are obtained after series of reactions under the synthesis temperature.(2) The molten salt synthesis route, previously reported to yield BaTiO3 nanowires was full of disputes and has been re-examined. The effects of surfactant, salt type, the ratio of mixed salts, annealing temperature and annealing time on the products’phase composition and morphology have been discussed. The results show that it is difficult to get BaTiO3 nanowires by molten salt synthesis method. The small amount of 1-D nanotructures in the sample can be indexed as BaTi2O5, BaTi5O11, BaTi3O7, Ba6Ti17O40 phases. None of the examined 1-D nanostructures in the sample could be indexed as BaTiO3. BaTiO3 is hard to grow anisotropically in the molten salt enviroment due to its high symmetry crystal structure. However, the BaTiO5, BaTi5O11, BaTi3O7,Ba6Ti17O40 phases with high anisometric crystal structures are more easily to form anisometric shapes. Based on above discussion, by adjusting the Ba/Ti ratio of the raw material and the process condition, pure phase one-dimensional Ba4Ti13O30 and BaTi5O11 nanomaterials were also obtained by molten salt synthesis method. This paper provides a new methodology for the synthesis of one-dimensional nanomaterial in BaO-TiO2 system.(3) One-dimensional BaTiO3 materials have been synthesized by template method. A new method based on templating and molten salt treatment is introduced to synthesize single-crystalline BaTiO3 nanowires. Pure phase single-crystalline BaTi2O5 nanowires were coated with BaC2O4·0.5H2O shell by the precipitation process. And then, the precursor was annealed in molten salt. Single-crystalline BaTiO3 nanowires were obtained finally. Compared with the BaTiO3 nanowires obtained by just annealing the precursor in air, the molten salt environment benefit the synthesis of BaTiO3 nanowires with perfect crystallinity. Besides, using K2Ti4O9 fibers as template, BaTiO3 fibers were obtained via the K2Ti4O9 fibers ion-exchanged with barium ions by hydrothermal process. Using H2Ti8O17 nanowires coated with BaC2O4·0.5H2O by a precipitation process as template, BaTiO3 nanowires were also obtained after annealed in air for a period of time. This kind of method is a self-sacrificial guide in-situ reaction, provides an efficient way to synthesis complex oxides with one-dimensional nanostructure. The coating process is a key factor in template synthesis of BaTiO3 nanowires.(4) The investigation of individual property of ferroelectric BaTiO3 and BaTi2O5 nanowires is still a challenge. The properties of individual BaTiO3 and BaTi2O5 nanowires were explored by SPM, Radiant Precision Workstation and nanomanipulate system. Piezoresponce force microscope measurements indicated that the d33* of BaTiO3 and BaTi2O5 were 15pm/V and 300 pm/V, respectively. BaTi2O5 has the better piezoresponce. The ferroelectric test along the nanowire’s diameter direction revealed that the Pr of BaTi2O5 is about 10 times bigger than BaTiO3 under the same voltage. And the test along the nanowire’s growth direction revealed that Pr of BaTi2O5 and BaTiO3 are similar. The Leakage current test of individual BaTi2O5 nanowires revealed that the leakage current obeyed the ohmic law under low voltage, and obeyed the space-charge limited current (SCLC) law under higher voltage. The conductivity value of BaTi2O5 nanowires is about 2×10-6 S/cm.更多还原