亚微米Beta-Li2TiO3的高稳定超胞结构：超临界水热场调制

As one of the key solid breeder materials in International Thermonuclear Experimental Reactor (IETR), fine Beta-Li2TiO3 with well-developed supercell structure has been a strategic focus to enhance the optimal tritium releasing properties in the pellet bed. This project aims to synthesize micro-sized Beta-Li2TiO3 with well developed supercell structure via hydrothermal reaction under supercritical conditions using anatase TiO2 and LiOH as raw materials, avoiding the destruction of the supercell structure promotion of the fine particles with further calcination for relative long time by the previously proposed wet-chemical methods. Aiding by the theoretical higher inner pressure, the lower viscosity, and the higher ion diffusion coefficients, the activation barrier of the stabilization of the ions in the supercell structure of Beta-Li2TiO3 can be effectively decreased, thus no further calcination is needed for the stabilization of the lithium and titanium ions, typically of the lithium ions in the (002) supercell lattice plane. Effects of the supercritical and sub-supercritical hydrothermal conditions on the supercell structure development and the experimental optimization for fine particles, and the necessary conditions concerning temperature, time, pressure, and concentration of the raw materials on the supercell structure stabilization and formation are referred to be investigated. Besides, sets of characterization methods for quantitative determination of the structure of Beta-Li2TiO3 and correlative complex compounds are to be explored by integrating the analysis of Frequency Spectrum of Fourier Transformation of High Resolution Transmission Electron Microscopy (HR-TEM) images, the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), Raman spectra and both the X-ray Diffraction (XRD) fine and simulated patterns. The project may aid the well understanding and thus providing the optimal experimental design for fine Beta-Li2TiO3 with well-developed supercell structure and further provide the theoretical solution to both the preparation and structure stability estimation of correlated complex oxides with multi-components. On the other hand, it is essential for future estimation of the enhancement of tritium proliferation and the stabilization when irradiated by heavy ions for Beta-Li2TiO3.

超胞结构高度稳定的超细Beta-Li2TiO3是极其重要的固态氚增殖新能源材料。本项目针对普通湿化学方法后期长时间煅烧容易破坏超胞结构的难题，提出利用超临界水热场调制直接制备高稳定的亚微米Li2TiO3。借助超临界水热场，有效降低超胞结构中离子稳定的活化势垒，旨在避免后期煅烧而直接促进超胞结构中Li和Ti离子归位并稳定。拟以TiO2和LiOH为原料，系统深入研究超临界水热场调制下超细颗粒可控制备的工艺优化并超胞结构高度稳定的必要条件及其形成机理。探索一套集成HR-TEM的傅里叶变换频率谱、ICP-AES、Raman光谱及XRD精细谱和模拟谱等测试方法定量评价复杂氧化物结构的方法。项目可为超临界水热场系统中制备高稳定超胞结构的Li2TiO3粉体提供直接工艺参数，可为同类复杂氧化物的制备及结构稳定性评价提供重要的理论参考，对提高Li2TiO3氚增殖性能和抗高能粒子轰击性能具有极其重要意义。

超胞结构高度稳定的超细Beta-Li2TiO3不仅是极其重要的固态氚增殖新能源材料，还在锂离子电池材料等领域中有重要应用。对亚微米颗粒的高稳定超胞结构的调控，是研究工作中的难点。项目针对普通湿化学方法后期长时间煅烧容易破坏超胞结构的难题，提出利用超临界水热场调制直接制备高稳定的亚微米Li2TiO3。以TiO2和LiOH为原料，系统深入研究了亚临界、超临界水热场调制下超细颗粒可控制备的工艺优化并超胞结构高度稳定的必要条件及其形成机理。还与普通水热场制备的材料进行了深入比较。探索了超临界及亚临界水热工艺参数，如：温度、时间、填充比（压力）及原料浓度对产物物相、超胞结构发育、晶粒尺寸及形貌均匀性的影响。通过析因分析，获得了晶粒尺寸小同时超胞结构发育良好的优化工艺。获得了不同超临界水热条件下粉体的Li/Ti值、Raman光谱及形貌，确定了缺陷类型。获得了亚稳结构和稳定结构的X射线精细谱及拟合谱，分析了不同超临界水热条件下的超胞结构。确定了升温过程中TiO2结构的变化并Beta-Li2TiO3的形成机理。获得了一定温度下，缺陷随时间的变化关系。确定了超胞发育的动力学方程。实现了制备粉体的X射线精细谱中积分强度I(002)/I(-133)值≥1.2，也即达到理论值的80%以上，同时控制晶粒尺寸在600nm以下的总体目标。三年的研究表明，超临界水热场调制下，层间Li离子可以有效归位，同时避免层内Ti离子扩散进入层间，这样直接解决了超胞发育完整的问题，避免了后期煅烧中结构的破坏。研究发现，水热温度和水热时间对Beta-Li2TiO3粉体性能影响显著。既能保证Beta-Li2TiO3粉体超胞发育良好，又能获得较小晶粒尺寸的水热合成工艺为：水热温度为375 °C，水热反应时间为10 h，初始Li+摩尔浓度为0.2 mol/L，填充比为50 %。此外，还发现一个特殊现象：375 °C时所得Beta-Li2TiO3粉体的超胞发育程度比400 °C条件下的好，且动力学参数K0和n值大，超胞发育速率快。总体而言，项目实践探索了一套定量评价复杂氧化物结构的方法。可为超临界水热场系统中制备高稳定超胞结构的Li2TiO3粉体提供直接工艺参数，可为同类复杂氧化物的制备及结构稳定性评价提供重要的理论参考，对提高Li2TiO3氚增殖性能和抗高能粒子轰击性能具有极其重要意义。