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诺贝尔化学奖得主丹·舍特曼教授讲座
2012-04-20 08:42   审核人:   (点击: )

2011年诺贝尔化学奖得主丹·舍特曼教授讲座通知 

讲座题目:准周期材料—重新定义的结晶体

Quasi-Periodic Materials – Crystal Redifined

讲座时间:2012年4月26日上午10:00

讲座地点:友谊校区国际会议中心第五会议室

主 讲 人:2011年诺贝尔化学奖得主丹·舍特曼教授

主讲人简介:

丹·舍特曼(Dan Shechtman,生于1941年,是出生于特拉维夫的以色列材料科学家。在以色列理工学院先后取得机械工程学士,材料科学硕士与博士学位。曾任以色列理工学院菲利普托比亚斯材料科学教授、美国能源部埃姆斯实验室(Ames Laboratory)助理、艾奥瓦州立大学材料科学教授。1982年4月8日,舍特曼在快速冷却的铝锰合金中发现一种新形态的二十面体相(Icosahedral Phase)分子结构,开辟了研究准晶体的全新领域。

2011年获诺贝尔化学奖,以表彰他对准晶体的发现。

准晶体,亦称为“准晶”或“拟晶”,是一种介于晶体和非晶体之间的固体结构。在准晶的原子排列中,其结构是长程有序的,这一点和晶体相似;但是准晶不具备平移对称性,这一点又和晶体不同。普通晶体具有的是二次、三次、四次或六次旋转对称性,但是准晶的布拉格衍射图具有其他的对称性,例如五次对称性或者更高的六次以上对称性。

关于这种长程有序的结构,数学家在1960年代就推测出了这种对称模型。但是直到快20年后这种理论上的结构才和准晶的研究联系起来。获得2011年诺贝尔化学奖的丹尼尔·舍特曼是第一个正式报道发现了准晶的人。1984年他和以色列理工学院的同事们在快速冷却的铝锰合金中发现了一种新的金属相,其电子衍射斑具有明显的五次对称性。这篇文章发表于物理评论通讯(Physical Review Letters )上。

讲座内容简介:

Crystallography has been one of the mature sciences. Over the years, the modern science of crystallography that started by experimenting with x-ray diffraction from crystals in 1912, has developed a major paradigm – that all crystals are ordered and periodic. Indeed, this was the basis for the definition of “crystal” in textbooks of crystallography and x-ray diffraction. Based upon a vast amount of experimental data, constantly improving research tools, and deepening theoretical understanding of the structure of crystalline materials no revolution was anticipated in our understanding the atomic order of solids.

However, such revolution did happen with the discovery of the Icosahedralphase, the first quasi-periodic crystal (QC) in 1982 and its announcement in 1984 [1, 2]. QCs are ordered materials, but their atomic order is quasiperiodic rather than periodic, enabling formation of crystal symmetries, such as icosahedral symmetry, which cannot exist in periodic materials. The discovery created deep cracks in this paradigm, but the acceptance by the crystallographers' community of the new class of ordered crystals did not happen in one day. In fact it took almost a decade for QC order to be accepted by most crystallographers. The official stamp of approval came in a form of a new definition of “Crystal” by the International Union of Crystallographers. The paradigm that all crystals are periodic has thus been changed. It is clear now that although most crystals are ordered and periodic, a good number of them are ordered and quasi-periodic.

While believers and nonbelievers were debating, a large volume of experimental and theoretical studies was published, a result of a relentless effort of many groups around the world. Quasi-periodic materials have developed into an exciting interdisciplinary science.

This talk will outline the discovery of QCs and discuss their structure as well as some of their properties.

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