Origin of the stability of quasicrystals: A experimental study of the random tiling model by means of high temperature x-ray diffraction

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Quasi-periodic lattice, which are basic structure of quasicrystals, is described as a projected lattice from the higher dimensional periodic lattice. Consequently atoms in the quasicrystals have six degree of freedom, three of which are the freedom of phonon and the others are those of phason. Phason fluctuation at higher temperature increases the entropy in term of atom positions, which means the decrease of free energy. In the real quasicrystalline systems the phason fluctuation may caused by the diffusion of atoms. The fact that many quasicrystals have large stable region of the composition at high temperature supports this model (random phason model). The objective of this study is to obtain directly experimental confirmation of the model by means of high temperature x-ray diffraction method.The intensities of the x-ray reflection in an icosahedral Al-Pd-Ru single quasicrystal were measured from room temperature to 800 C on BLO8W in Japan Synchrotron Radiation Research Institute. From the result, (1) each intensity decreased drastically at 500-600 C and (2) the change of the intensity showed the hysteresis curve against temperature.A new sample stage in which specimen can be held up to 1000 C has been designed and made for laboratory x-ray equipment It can be attached to normal (small) 4 circle goniometer although the mobile angular region of it is restrained.