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，被描述为高维周期晶格的投影晶格。因此，准晶中的原子有六个自由度，其中三个是声子的自由度，其余的是相子的自由度。在较高的温度下，相子涨落增加了原子位置的熵，这意味着自由能的降低。在实际的准晶系统中，原子的扩散可能会引起相子涨落。许多准晶在高温下具有较大的成分稳定区，这一事实支持这一模型(随机相子模型)。本研究的目的是通过高温X射线衍射法直接对该模型进行实验验证。在日本同步辐射研究所的BLO8W上测量了二十面体Al-Pd-Ru单晶从室温到800℃的X射线反射强度。结果表明：(1)在500-600℃温度范围内，各光强急剧下降；(2)光强随温度的变化呈滞后曲线。为实验室X射线设备设计并制作了一种新的样品工作台，它可以固定在普通(小)四圆测角仪上，但其活动角区受到限制。

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.