Studies on controle method of structural and physical properties of quasicrystals

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In order to clarify physical properties of a quasicrystal, we have carried out careful investigation of quasicrystal structure and the relation between the structural perfection of quasicrystals and the physical properties such as magnetic susceptibility, electrical resistivity and magneto resistance. The Al-Pd-Mn and Zn-Mg-Ho quasicrystals were selected for this purpose, both of which belong to so-called "ideal quasicrystal" group. With respect to the Al-Pd-Mn, it was found that the F-type icosahedral quasicrystal, which is stable at high temperature, becomes unstable below approximately 750 C, and transforms to a complicated modulated quasicrystal at the alloy composition of Al71Pd21 Mn8.On the Zn-Mg-Ho icosahedral quasicrystals, it was discovered that the degree of F-type chemical ordering depends on the alloy composition ; highly ordered state realized only near the composition of Zn60Mg30Ho10. Further, increase of annealing temperature causes decrease in the intensity of superlattice reflections in the X-ray diffraction pattern. It was experimentally shown that the decreuse of the intensity is related to change of behavior of electrical resistivity and magneto resistance. This result opened the new controlling method of physical properties of quasicrystals by changing chemical ordering and thus degree of perfection of quasiperiodicity.