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Microscopic Theory of Quasicrystal-Crxrstal Transformation

准晶-晶体转变的微观理论

基本信息

批准号：
13640373
负责人：
ISHII Yasushi
金额：
$ 1.79万
依托单位：
CHUO UNIVERSITY
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 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640373/
关键词：
quasicrystal structure transformation approximant crystal phason elasticity electronic structure 擬ギャップ

项目摘要

Structural models for decagonal Al-Ni-Co quasicrystals have been studied by Monte-Carlo calculations, in which a swap of nearby atoms of different species and reshuffling of the three rhombi in a fat and thin hexagons in quasiperiodic tiling are considered. We have done systematic studies of the tiling and the atomic decoration as a function of the atomic composition. We find that a framework of the HBS tiling with Al atoms on vertices does not change within a reasonable range of the Al composition change. Here the HBS tiling is a pattern consisting of hexagon (H), boat (B) and star (S) tiles with appropriate atomic decoration. For higher Co composition, a structure with a decagonal tile is obtained. Such a decagonal pattern is stabilized by the more attractive interaction between Al and Co than that between Al and Ni.Besides the studies of structural models of quasicrystals, we have done first-principles studies of electronic structures of approximant crystals for recently discovered Cd-and Zn-based quasicrystals. It is found that low-lying unoccupied d-states coming from an element forming compounds with Cd and Zn are important for formation of pseudogap in the electronic density of states. Although origin of the pseudogap in quasicrystals and approximants has been discussed in a framework of a nearly-free electron model (the Hume-Rothery mechanism), the present results show that choice of chemical species is essential not only for controlling the valence electron density but for the pseudogap formation. Using quantity called "crystal orbital Hamilton population", we find that the bonding nature of wavefunctions is changed from bonding to antibonding at the pseudogap. This observation suggests that the electronic structures of Cd-and Zn-based compounds are very different from ordinary alloys and more similar to semiconductors.

用蒙特-卡罗方法研究了Al-Ni-Co准晶的结构模型，考虑了不同种类原子的交换和准周期镶嵌中三个菱形在一个胖六边形和一个瘦六边形中的重排。我们已经做了系统的研究，瓷砖和原子装饰作为一个功能的原子组成。我们发现，一个框架的HBS平铺与Al原子的顶点不改变在一个合理的范围内的Al组成的变化。这里的HBS平铺是由六边形（H）、船形（B）和星星（S）平铺组成的图案，并带有适当的原子装饰。对于更高的Co成分，获得具有十边形瓦的结构。Al和Co之间的相互作用比Al和Ni之间的相互作用更有吸引力，从而稳定了这种十边形结构。除了准晶结构模型的研究之外，我们还对最近发现的Cd基和Zn基准晶的近似晶体的电子结构进行了第一性原理研究。结果表明，与Cd、Zn形成化合物的元素所产生的低能级未占d态对电子态密度赝能隙的形成起着重要的作用。虽然准晶体和近似物中的赝能隙的起源已经在近自由电子模型（Hume-Rothery机制）的框架中进行了讨论，但目前的结果表明，化学物种的选择不仅对于控制价电子密度而且对于赝能隙的形成是必不可少的。利用“晶体轨道汉密尔顿布居”量，我们发现在赝能隙处波函数的成键性质由成键变为反键。这一观察结果表明，Cd和Zn基化合物的电子结构与普通合金非常不同，而更类似于半导体。