【作者】 刘美男；

【导师】 薛冬峰；

【作者基本信息】 大连理工大学 ， 化学工艺， 2009， 博士

【摘要】 铌酸锂因具有优良的电学和光学特性引起了世界范围内科学家的广泛研究兴趣。如何有效控制铌酸锂的成核、生长,进而实现对其化学组成、微观形貌、晶格结构乃至物理性质的调控,对于深入研究结构与物性的关联,并最终实现按照人们的意愿设计合成功能材料具有重要意义。本论文对于铌酸锂的一维和三维微纳米结构的设计合成、形成机制以及近化学计量比铌酸锂的液相、固相合成新方法等方面进行了有益的探索。论文设计了有机配体调控微观形貌的液相合成策略,并成功地应用到铌酸锂一维微米棒和三维微米空心球的合成中。通过探讨有机配体的几何构型与产物微观形貌的关联,发现通过选择不同种类的有机配体能够实现对铌酸锂微观结构的有效剪裁,为调控其他铌酸盐的微观形貌提供了有益参考。另外,本论文还对铌酸锂的光学性质进行了初步研究,结果表明不同形貌的铌酸锂具有不同的禁带宽度;通过对微观形貌的剪裁能实现对其光学性能的有效调控。论文采用固相燃烧法制备铌酸锂微晶。在反应过程中,尿素既作为燃烧剂又作为高活性配体与原料络合,从而大幅度降低了反应活化能,实现了在较低温度下铌酸锂的合成。通过对实验参数的系统考察,给出了铌酸锂的最佳合成条件:反应温度为500-600℃,尿素与原料（铌源和锂源）的质量比为3:1-4:1,反应时间为2.5-4 h。论文开发了自牺牲模板法制备五氧化二铌空心球和铌酸锂空心球的工艺路线。首先设计具有中空结构的铌前驱物H₂（H₂O）Nb₂O₆,而后分别通过脱水过程和固相燃烧过程实现了五氧化二铌空心球以及铌酸锂空心球的制备。紫外光谱结果表明,与体块铌酸锂以及溶剂热法合成的铌酸锂空心球相比,采用前驱物法合成的铌酸锂空心球缺陷较少。基于对空心球生长机制的分析,发现前驱物比较活泼,容易与其他金属离子发生反应,因而自牺牲模板法也同样适用于合成其他中空结构的铌酸盐。论文深入研究了化学合成方法在制备近化学计量比组分铌酸锂中的应用。详细探讨了在固相燃烧合成反应中加热速率对产物组分的影响,发现随着加热速率的降低,铌酸锂中的锂缺陷减少。在5-10℃/min的加热速率条件下能够获得高品质的铌酸锂。另外,由于有机配体与金属离子络合能够有效抑制锂组分的挥发,因而溶胶凝胶法也被证明是合成近化学计量比铌酸锂的有效途径。更多还原

【Abstract】 Lithium niobate has drawn continuous research attention due to its excellent electric and optical properties. The main challenge in this area is how to precisely control morphologies, compositions, and crystal structures, and thus effectively tailor its physical and chemical properties in a controllable way. In this PhD dissertation, some experimental work has been carried out on the synthetic methods including both solution and solid-state reaction routes, to prepare near-stoichiometric lithium niobate and to design one- and three-dimensional lithium niobate micro/nano-structures. The formation mechanisms of various lithium niobate products were also proposed. The main results are summarized herein:One-dimensional rods and three-dimensional hollow spheres of lithium niobate have been fabricated in a versatile amine-assisted hydrothermal system. Various morphologies could be achieved by selecting ligands with different geometrical structures. Additionally, the optical properties of lithium niobate with different morphologies have also been investigated. It has been found that the optical property can be well tuned by adjusting the morphology.Solid-state combustion method has been developed to prepare lithium niobate. In the reaction, urea plays two roles: one is as a combustion reagent, and the other is to coordinate with raw materials, which abruptly reduces the reaction active energy. The operation parameters were comprehensively studied, and the optimal operation parameter has been proposed: reaction temperature about 500-600°C; quantity ratio of urea to raw materials （niobium source and lithium source） about 3:1-4:1; reaction time about 2.5-4 h.A sacrificial template method has been developed in the current work to fabricate niobium oxide and lithium niobate with hollow structure. First, a novel niobium-based precursor H₂（H₂O）Nb₂O₆ with hollow architecture has been designed, and then niobium oxide and lithium niobate hollow spheres were obtained through a dehydration process and a combustion treatment, respectively. The optical analysis results demonstrate that the hollow spheres obtained by this combustion process show high quality, compared with those lithium niobate bulk and lithium niobate hollow spheres fabricated through a solvothermal system. Furthermore, this method can be extended into the fabrication of other niobates with hollow structure due to the high reactivity of precursor. Chemical synthesis methods have been studied on the preparation of near-stoichiometric lithium niobate powders. The effect of heating rate on the composition of products has been studied in detail and the conclusion is that the lithium defect decreases with reducing the heating rate, and under the heating rate of 5-10℃/min, the high quality lithium niobate can be obtained. In addition, the sol-gel method has also been confirmed to be an effective route for fabricating high quality lithium niobate considering that the ligand well coordinates with metal ions, thus effectively protect the lithium lattice.更多还原