Atomic and Electronic Structure of Ceramic Bicrystals and High Temperature Strength

陶瓷的力学性能与晶界的原子结构和化学键状态密切相关。因此，需要弄清性能与晶界结构之间的关系，以便为设计高强度、高可靠性的陶瓷提供指导。本论文系统地研究了陶瓷双晶的制备、晶界原子和电子结构的评价、晶界特征与晶界滑移、晶界偏析的影响，得到了以下结果：1.陶瓷的制备通过高温连接两个单晶，得到了具有[110]倾斜晶界的氧化锆双晶和具有[1120]倾斜晶界的氧化铝双晶。用原子力显微镜观察了它们的热槽分布，测量了它们的晶界能。结果表明，晶界能与晶界…有关。2.晶界原子和电子结构的评估结合高分辨电子显微镜图像和图像模拟技术确定了双晶中晶界原子结构。将所得结构与分子轨道法推导出的原子结构进行了比较。实验结果与理论分析结果吻合较好。3.晶界特征与晶界滑移研究发现晶界滑移受晶界特征的影响。而晶界滑移主要受晶界原子构型的控制，而不是晶界能量的控制。4.晶界偏析的影响用场发射电子显微镜的纳米探针用能谱仪和能谱仪研究了晶界偏析。结果表明，偏析过程中的化学成分和化学键状态强烈依赖于晶界特征。通过比较EELS谱和分子轨道方法计算的偏态密度来评价晶界化学键状态。较少

Mechanical properties of ceramics are closely related to the atomic structure and chemical bonding state in the grain boundaries. Therefore, the relationships between properties and grain boundary structure are needed to be clarified in order to obtain a guideline to design high strength and high reliable ceramics. In this study, 1 : Fabrication of ceramics bicrystals, 2 : Evaluation of grain boundary atomic and electronic structure, 3 : Grain boundary characteristics and grain boundary sliding, and 4 : Effect of grain boundary segregation were systematically investigated and the following results were obtained.1 : Fabrication of ceramicsZirconia bicrystals with [110] tilt boundaries and alumina bicrystals with [1120] tilt boundaries were fabricated by joining two single crystals at high temperatures. Their grain boundary energy was measured by observing the profiles of thermal grooving by an atomic force microscope. It was found that the grain boundary energy depends on the grain boun … More dary characteristics and shows the energy cusp at the tilt angles corresponding to CSL orientation.2 : Evaluation of grain boundary atomic and electronic structureGrain boundary atomic structures in the bicrystals were determined by combing HREM image and the image simulation technique. The obtained structures were compared with the atomic structures deduced by molecular orbital method. The experimental results agreed well with the theoretically obtained structures.3 : Grain boundary characteristics and grain boundary slidingIt was found that the grain boundary sliding were influenced by the grain boundary characteristics. However, grain boundary sliding is mainly controlled by the grain boundary atomistic configuration, rather than grain boundary energy.4 : Effect of grain boundary segregationGrain boundary segregation was investigated by EDS and EELS by using nano probe in a field emission electron microscope. It was found that the chemical composition and chemical bonding state in the segregation strongly depended on the grain boundary characteristics. Grain boundary chemical bonding state was evaluated by comparing the EELS spectra and partial density of state calculated by the molecular orbital method. Less