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，是高维周期晶格的投影晶格。因此，准晶体中的原子具有六个自由度，其中三个是声子的自由度，其余的是相子的自由度。较高温度下的相子波动使原子位置上的熵增加，这意味着自由能的减少。在实际的准晶体系中，原子的扩散会引起相位波动。许多准晶体在高温下具有较大的稳定区，这一事实支持了该模型（随机相子模型）。本研究的目的是利用高温x射线衍射法对该模型进行直接的实验验证。用日本同步辐射研究所的BLO8W测量了二十面体Al-Pd-Ru单晶在室温至800℃范围内的x射线反射强度。结果表明：(1)在500 ~ 600℃时，各强度急剧下降；(2)强度随温度的变化呈滞后曲线。为实验室x射线设备设计并制造了一种新的样品台，该样品台可将样品保持在1000℃以下，它可以连接到普通（小）4圆测角仪上，尽管它的可移动角区域受到限制。