Dislocations in quasicrystals

在准晶体中，我们可以定义一个位错，它的Burgers向量是一个四维或更高维晶格的晶格平移向量。这种位错是准晶体固有的一种新型结构缺陷，它不仅伴随着常规应变，而且伴随着一种称为相应变的应变，这种应变是由正交于实空间的互补空间中的晶格畸变引起的。为了澄清这种位错的性质，我们进行了以下研究。首先，我们对二十面体（i-） Al-Pd-Mn和十面体（d-） Al-Ni-Co进行了塑性变形实验。在这两种样品中，都观察到准晶中常见的功软化现象。通过热活化分析，我们假设位错的拖拽应力随温度变化，系统地分析了不同温度下的数据。其次，我们研究了在准晶体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观察了相缺陷的结构，ii)我们在高温下测量了比热来研究热平衡相，iii)我们用原位高温HRTEM观察了在高温下运动的相。在i)中，我们通过STM观察到d-Al-Ni-Co中存在冻结相缺陷。在ii)中，我们用DSC测量了i-Al-Pd-Mn和d-Al-Cu-Co的比热（Cp）。我们观察到Cp与3k/原子的Dulong-Petit值（k: Boltzman常数）有一个向上的偏差，在800℃左右达到5k。这可以解释为相子的热激发。我们计算了Cp增量的熵变，并将其与计算机模拟结果进行了比较。在iii)中，我们首次用HRTEM直接观察到运动相。

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.