本论文围绕纳米晶钛酸钡颗粒材料的研究展开，独创了“一步溶胶法”，在低温下制备出了晶粒尺寸小于10nm的一系列高结晶度钛酸钡粉体及颗粒薄膜，系统地对10nm以内小尺寸钛酸钡的相结构及物理性能展开了研究，探讨了钛酸钡维持铁电性的极限尺寸，并成功地将其应用在储能薄膜和镍粉包覆技术，实现了钛酸钡纳米晶颗粒材料的有效应用。通过对钛酯水解-交联反应速率的精准控制，独创了介于溶胶凝胶法和沉淀法之间的“一步溶胶法”，常压下制备出了平均晶粒尺寸小至2.8nm的结晶型钛酸钡颗粒及其稳定溶胶。该方法成功地应用于方形钛酸锶纳米晶及其稳定溶胶的制备。采用该稳定溶胶在160℃的低温下制备出了高结晶度的钛酸盐颗粒薄膜。利用拉曼、同步辐射衍射、成对分布函数（PDF）和X射线光电子能谱（XPS）分析发现小至2.8nm的钛酸钡颗粒呈现多相共存的结构特征，非中心对称相含量与颗粒表面结构密切相关。其相变过程十分弥散，分布在较宽的温度范围内，且非中心对称的四方、正交相结构在400℃的高温下依然存在，首次证实了小至2.8nm的钛酸钡颗粒依然具有铁电性。对纳米晶钛酸钡颗粒进行了一系列的物理性能分析表征。二次谐波产生（SHG）实验证实了这些纳米晶颗粒在室温下具有非线性极化效应，并且SHG响应随温度的升高逐渐下降，呈现出由非中心对称的铁电相结构逐渐向顺电相转变的趋势。颗粒在外加电场下的极化翻转行为和介电性能测试均进一步证实了小至2.8nm的钛酸钡颗粒具有铁电性。最后本文对这些纳米晶颗粒在多方面的应用进行了探索。利用获得的稳定溶胶在≤160℃的低温下制得了高结晶度的钛酸盐颗粒薄膜，薄膜呈现良好的介电特性和温度稳定性；通过多层化结构设计，具有铁电性的8nm钛酸钡颗粒在有机-无机复合材料中获得了高的电位移极化，有效地实现了复合薄膜的高击穿场强（495kV/mm）和储能密度（19.37J/cm3）；将纳米晶钛酸钡材料的制备方法应用于镍粉表面的包覆改性，通过快速高效的一步反应形成了致密均匀的钛酸钡多晶包覆层，有效延缓了纳米镍粉的烧结收缩并改善了其抗氧化性能。
This dissertation mainly focuses on study of the finite-dimensional barium titanate nanoparticles (BTO NPs). An original “one-step sol” method was developed to synthesize a series of BTO NPs and films within 10 nm crystal size. Phase structure and physical properties of the BTO NPs, including the ferroelectric critical size, were systematically investigated. These NPs were successfully applied in preparing high energy-storage nanocomposite thin films and coating of nickel particles.By controlling the hydrolysis vs. crosslinking rate, “one-step sol” method, which lies between the sol-gel and precipitation method, was designed to fabricate BTO NPs with crystal size as small as 2.8 nm and their highly stable sols. Strontium titanate nanocubes and sol were also obtained by this method. Moreover, these stable sols were utilized to fabricate highly crystallized nanoparticle films under 160 °C.The results of Raman, synchrotron X-ray diffraction, pair-distribution function (PDF) analyses and X-ray photoelectron spectroscopy (XPS) confirmed that BTO NPs even as small as 2.8 nm are ferroelectric with multi-phase coexistence. And the non-centrosymmetric phases were highly related to the surface structures of the NPs. Diffused phase transition characters over a wide temperature range were observed. The non-centrosymmetric phases even persisted at temperatures as high as 400 °C. Measurements of second harmonic generation (SHG), ferroelectric response and dielectric properties further confirmed the ferroelectricity of these BTO NPs. SHG signals, which showed a non-linear polarization effect at room temperature, declined with the increase of the temperature, revealing a successive transition from the non-centrosymmetric ferroelectric phases to paraelectric ones. Dielectric measurements and the ferroelectric polarization switching behavior in response to the applied external electric field further confirmed the ferroelectricity of these BTO NPs.Several applications of the ferroelectric BTO NPs were investigated. Firstly, titanate nanoparticle thin films with excellent dielectric properties and high temperature stability were fabricated using the nanocrystal sols under 160 °C; secondly, with the 8 nm BTO NP fillers, the multilayer nanocomposite films achieved large electric displacements, high breakdown strength (Eb=495kV/mm) and high energy storage densities (Ue=19.37J/cm3); finally, a dense and uniform BTO polycrystalline coating layer was obtained on nickel NPs by the modified “one-step sol” method, and this layer was proved to be effective in improving the shrinkage behavior and anti-oxidation properties of the nickel NPs during sintering.
