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

准晶稳定性的起源：高温X射线衍射随机平铺模型的实验研究

• 批准号: 13640380
• 负责人: WATANABE Yasuhiro
• 金额: $ 2.37万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640380/
• 关键词: quasicrystal; phason; high temperature; x-ray diffraction; random phason model; synchrotron radiation; Al-Cu-Ru; Al-Pd-Ru

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.

准周期晶格是准晶体的基本结构，被描述为来自较高维度周期晶格的投影晶格。因此，准晶体中的原子具有六个自由的自由，其中三个是声子的自由，而其他的是帕森的自由。在较高温度下的Phason波动会增加原子位置的熵，这意味着自由能的减少。在实际的准晶体系统中，Phason波动可能是由原子的扩散引起的。许多准晶体在高温下具有较大稳定区域的事实支持了该模型（随机Phason模型）。这项研究的目的是通过高温X射线衍射方法直接获得模型的实验确认。从结果开始，（1）每个强度在500-600 c时急剧下降，（2）强度的变化显示出在温度下的磁滞曲线。一个新的样品阶段，可以将标本可保持到1000 c的新样本阶段，并用于实验室X射线设备，它可以连接到正常的（小）4个圆形圆锥体仪，尽管它是4个圆形圆锥体的，但它的移动角度是限制的。