High Angular Resolution Electron Channeling X-ray Spectroscopy for Radiation-Induced Local Disordering in Magnesium Aluminate Spinel Compounds

高角分辨率电子通道 X 射线光谱分析镁铝尖晶石化合物中辐射引起的局部无序

• 批准号: 12450260
• 负责人: MATSUMURA Syo
• 金额: $ 10.62万
• 依托单位: Kyushu University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450260/
• 关键词: Radiation damage; Spinel crystals; Electron diffraction; Electron channeling; ALCHEMI; Fusion materials; Disordering; Radiation effects; 結晶構造因子; X線分光; 内殻電子励起非弾性散乱

This project aimed to promote basic understanding of radiation-induced structural change in magnesium aluminate spinel compounds (MgO-nAl_2O_3), which are drawing much attention as candidates for radiation resistant materials in future nuclear programs. To this end, we developed a new experimental technique of transmission electron microscopy to analyze quantitatively local atomic configuration. Then the technique, which is called as high angular resolution electron channeling x-ray spectroscopy (HARECXS), was applied to MgO-nlAl_2O_3 irradiated with 1 MeV Ne^+ or 500 keV He^+ ions to disclose ion displacements involved in structural disordering. The project started in FY 2000 with examination of HARECXS as a practical tool to locate lattice ions in spinel compounds. In the procedure of HARECXS, characteristic x-ray emission from an electron-illuminated local specimen area is measured as a function of the electron beam direction with high angular resolution. The theoretical arguments b … More ased on the dynamical electron diffraction and inelastic scattering clearly showed that the HARECXS profiles of x-ray intensity variations thus obtained sensitively depends on not only ion-configuration but also specimen thickness and Debye-Waller factors. From the profiles, one can determine accurately the occupation probabilities of constituent ions on specific sites in the crystal lattice. In the next two years, the research work was mostly focused on partially ordered states in as-grown crystals and evolution of structural disordering under ion irradiation. In MgO-nAl_2O_3 with n=1.0 and 2.4, most Al^<3+> lattice-ions occupy the octahedral (VI) sites with 6-fold coordination, while Mg^<2+> lattice-ions reside on both the tetrahedral (IV) and the octahedral (VI) sites. The structural vacancies are enriched in the IV-sites. Irradiation with 1 MeV Ne^+ ions causes disordering of cation configuration in the pre-peak damaged range without any defect cluster formations, while it displaces not only cations but also anions from their crystallographic sites and forms small defect clusters in the peak-damaged area. It is suggested that the structural vacancies due to nonstoichiometry for n=2.4 take part in recombinations with displaced ions. Irradiation with 500 keV He^+ causes less disordering than 1 MeV Ne^+ irradiation does. A higher ionizing rate under the former condition is ascribed to the less disordering tendency, since recovery or reordering is more promoted with ionization-enhanced migration of displaced ions. Less

镁铝尖晶石化合物（MgO-nAl_2 O_3）是一种新型的抗辐射材料，在核工业中具有重要的应用前景。为此，我们发展了一种新的实验技术，透射电子显微镜定量分析局部原子构型。利用高角分辨电子沟道X射线能谱（HARECXS）技术研究了1 MeV Ne^+或500 keV He^+离子辐照MgO-nlAl_2 O_3晶体后的离子位移。该项目于2000财政年度开始，将HARECXS作为确定尖晶石化合物中晶格离子位置的实用工具。在HARECXS的过程中，从电子照射的局部试样区域的特征X射线发射测量作为具有高角分辨率的电子束方向的函数。理论论据B ...更多信息 基于动态电子衍射和非弹性散射的结果表明，由此得到的X射线强度变化的HARECXS轮廓不仅敏感地依赖于离子组态，而且还依赖于样品厚度和Debye-Waller因子。根据这些分布，可以准确地确定晶格中特定位点上组成离子的占据概率。在接下来的两年中，研究工作主要集中在生长晶体中的部分有序态和离子辐照下结构无序的演化。在n=1.0和2.4的MgO-nAl_2 O_3中，Al^<3+>晶格离子主要占据六配位的八面体（VI）位置，而Mg^<2+>晶格离子则同时占据四面体（IV）和八面体（VI）位置。结构空位在IV位富集。1 MeV Ne^+离子的照射会导致峰前损伤范围内的阳离子构型无序，而不会形成任何缺陷团簇，同时它不仅会将阳离子而且还会将阴离子从其晶体学位置上取代，并在峰损伤区域形成小缺陷团簇。它建议，由于非化学计量n=2.4的结构空位参加与位移离子的重组。500 keV He^+辐照引起的无序度小于1 MeV Ne^+辐照引起的无序度。在前一种条件下较高的电离速率归因于较小的无序化倾向，因为恢复或重新排序更促进与电离增强迁移的位移离子。少