Structural study on quasicrystals and their approximants in the Al-Ni-Co alloy system, by means of anomalous X-ray scattering

点击翻译按钮获取中文摘要

The Al-Ni-Co decagonal phase has received much attention, because, of several modulations of decagonal quasicrystals, showing highly-ordered diffraction patterns or several different type of diffraction patterns with super-lattice reflections, and some crystalline approximants. In order to reveal the structures of these decagonal quasicrystals, many studies have been made by electron diffraction analysis, high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAERDF-STEM). However, previous studies have been made on individual decagonal quasicrystals, and no systematic interpretation on the structures of all the Al-Ni-Co decagonal quasicrystals has been performed. This research project has performed precise structural analysis of a crystalline approximant, which is found in alloy around Al_<72.5>Ni_<17>Co_<20.5>, annealed at 950℃. The structure of this W-(AlCoNi) phase, enables us to discuss the str … More uctures of the Al-Ni-Co decagonal quasicrystals in detail. These research results can be referred as one of the most important structural information considering the quasicrystals and related approximant crystals and the head investigator was invited to International Conference of Quasicrystals 2001.The present research project developed the relatively new technique of single crystal anomalous X-ray scattering technique, which prompts us to know fine structure around a specific element in an alloy sample. This, new analytical tool succeeded to characterize the distribution of Cu in the Al-Cu-Fe approximant phase and allowed us to understand the structural role for Cu for the formation of approximant phase related to quasicrystals.The present research group has also performed the systematic research with respect to structures of cubic approximant phase with large icosahedarl atom clusters. The obtained results were demonstrated in the International Workshop for Quasicrystals as a key lecture. Less