Atomic and Electronic Structure of Ceramic Bicrystals and High Temperature Strength

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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