Dislocations in quasicrystals

在准晶中，我们可以定义一种位错，其Burgers矢量是四维或更高维晶格的晶格平移矢量。这种位错是准晶固有的一种新型结构缺陷，它不仅伴随着传统的应变，还伴随着一种称为相变的应变，这种应变是由与实空间垂直的余空间中的晶格扭曲引起的。为了弄清这种位错的性质，我们进行了以下研究。首先，我们进行了二十面体(i-)Al-Pd-Mn和十方(d-)Al-Ni-Co的塑性变形实验。在这两个样品中，都观察到了准晶常见的功软化现象。作为热激活分析的结果，我们系统地分析了不同温度下的数据，假设位错的拖曳应力与温度有关。其次，我们研究了准晶中位错动力学性质中起重要作用的相子的结构和性质。在这里，i)我们用STM观察了相子缺陷的结构，ii)我们测量了高温下的比热来研究热平衡的介子，iii)我们用原位高温HRTEM观察了高温下相子的运动。在I)中，我们用扫描隧道显微镜观察到了d-Al-Ni-Co中的冻结相子缺陷。利用差示扫描量热法(DSC)测量了i-Al-Pd-Mn和d-Al-Cu-Co的比热。我们观察到Cp从3K/原子的杜龙-珀提值(k：玻尔兹曼常数)向上偏离，并在大约800℃时达到5K。这可以解释为相子的热激发。我们计算了由CP的增量得到的熵变，并将其与以前的计算机模拟结果进行了比较。在第三章中，我们首次用高分辨电子显微镜直接观测到了运动中的声子。

In quasicrystals, we can define a dislocation whose Burgers vector is a lattice translational vector of a 4D or higher dimensional lattice. Such a dislocation is a novel type of structural defect inherent to quasicrystal in the sense that it is accompanied not only by a conventional strain but also by a strain named phason strain which is caused by a lattice distortion in a complementary space orthogonal to real space. We performed the following researches for the purpose of clarifying the properties of such a dislocation. First, we perfomed plastic deformation experiments for icosahedra (i-) Al-Pd-Mn and decagonal (d-) Al-Ni-Co. For both samples, work softening, which is generally seen for quasicrystals, was observed. As a result of thermal activation analysis, we analyzed the data at various temperatures systematically on the assumption of temperature-dependent dragging stress for a dislocation. Second, we investigated structure and properties of phasons, which play an important role in the dynamical property of the dislocation in quasicrystals. Here, i) we observed the structure of a phason defect by STM, ii) we measured specific heat at high temperatures to investigate thermally equilibinium phasons and iii) we observed the phasons in motion at high temperatures by in-situ high-temperature HRTEM. In i), we observed a frozen-in phason defect in d-Al-Ni-Co by STM. In ii), we measured specific heat (Cp) of i-Al-Pd-Mn and d-Al-Cu-Co by DSC. we observed an upward deviation of Cp from the Dulong-Petit value of 3k/atom (k : Boltzman's constant) and it reached 5k at about 800℃. This can be interpreted as a thermal excitation of phasons. We calculated the entropy change from the increment of Cp and compared it with the result of the computer simulations previously done. In iii), we observed directly phasons in motion by HRTEM for the first time.