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

准周期晶格是准晶的基本结构，它被描述为从高维周期晶格投影出来的晶格。因此，准晶中的原子有六个自由度，其中三个是声子自由度，其余的是相子自由度。高温相位子涨落使原子位置熵增大，自由能减小。在真实的准晶系统中，原子的扩散可能引起相子涨落。许多准晶在高温下具有大的组成稳定区的事实支持这个模型（随机相子模型）。本文利用日本同步辐射研究所的BLO 8 W高温X射线衍射仪，测量了Al-Pd-Ru二十面体准晶单晶体从室温到800 ℃的X射线反射强度，为直接从实验上证实该模型提供了依据。实验结果表明：（1）在500-600 ℃时，各强度均急剧下降;（2）强度随温度的变化呈滞后曲线。本文设计并制作了一种可在1000 ℃下放置样品的新型样品台，它可安装在普通（小型）四圆测角仪上，但其移动的角度范围受到限制。

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.