Geometric Frustration of Icosahedron in Metallic Glasses
Geometric Frustration of Icosahedron in Metallic Glasses
复制标题
金属玻璃中二十面体的几何挫败
DOI：
10.1126/science.1232450
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发表时间：
2013-07-26
期刊：
影响因子：
56.9
通讯作者：
Chen, M. W.
中科院分区：
文献类型：
--
作者：
Hirata, A.;Kang, L. J.;Chen, M. W.
有序，有序玻璃质材料的结构一直是一个谜，人们知道它有短程有序，但没有长程模式。目前的一种理论是，一些玻璃质材料具有二十面体有序性，这种基序无法显示平移周期性。平田等人（第376页，7月11日在线发表）从金属玻璃的亚纳米体积中获得了衍射图案，这些图案显示了二十面体的一些（但不是全部）预期特征。模拟表明，图案产生的二十面体扭曲，包括面心立方结构的功能。这一观察结果与分子动力学模拟的预测不同，并为理解全球廉价长程有序和局部廉价短程有序之间的竞争提供了关键信息。大块金属玻璃中的小体积区域显示出由部分面心立方对称性扭曲的二十面体有序。二十面体有序被认为是半个多世纪以来过冷液体和金属玻璃中普遍存在的原子模式，因为二十面体是高度紧密堆积的，但由于结构挫折和缺乏平移周期性而难以生长。本文报道了用单二十面体的电子衍射方法对金属玻璃中局部二十面体有序性的实验观察。所有检测到的二十面体被发现是扭曲的部分面心立方对称，提出了令人信服的证据几何挫折的局部二十面体秩序的金属玻璃。
Order, Order The structure of glassy materials, which are known to have short-range order but no long-range pattern, continues to be a puzzle. One current theory is that some glassy materials possess icosahedral ordering, a motif that cannot show translational periodicity. Hirata et al. (p. 376, published online 11 July) obtained diffraction patterns from subnanometer volumes in a metallic glass, which show some, but not all, of the expected features of an icosahedron. Simulations suggest that the patterns arise from icosahedrons distorted to include features of the face-centered cubic structure. This observation is different from the predictions of molecular dynamics simulations and provides pivotal information in understanding the competition between the formation of the globally inexpensive long-range order and the locally inexpensive short-range order. Small-volume regions in a bulk metallic glass show icosahedral ordering distorted by partial face-centered cubic symmetry. Icosahedral order has been suggested as the prevalent atomic motif of supercooled liquids and metallic glasses for more than half a century, because the icosahedron is highly close-packed but is difficult to grow, owing to structure frustration and the lack of translational periodicity. By means of angstrom-beam electron diffraction of single icosahedra, we report experimental observation of local icosahedral order in metallic glasses. All the detected icosahedra were found to be distorted with partially face-centered cubic symmetry, presenting compelling evidence on geometric frustration of local icosahedral order in metallic glasses.