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| column | value |
|---|---|
| 講者姓名 | Dan Shechtman |
| 服務機構 | Professor of Israel Institute of Technology, Haifa, ISRAEL |
| 演講時間 | 2012-05-07 |
| 演講題目 | Quasi-Periodic Materials |
| 摘要 | Modern crystallography since 1912 defines that &ldquo;crystals&rdquo; were ordered and periodic. It required the crystals to bear only 1, 2, 3, 4, and 6. 5-fold rotational symmetry as well as any other symmetry beyond 6 is forbidden in periodic structures.<br /> <br /> In 1982, 70 years after the study of crystallography, quasi-periodic crystals were discovered. Prof. Dan Shechtman first observed an icosahedral phase in Al6Mn and identified a 5-fold diffraction pattern under Transmission Electron Microscope (TEM).<br /> <br /> Prof. Shechtman underwent detailed experiments to confirm the relation of the 2-, 3-, and 5-fold rotational symmetry axes using TEM. He and his colleagues also demonstrated the quasi-periodicity of such materials using Fibonacci series.<br /> <br /> However, his claims were rejected by the community of crystallographers in the years between 1982 and 1987. In 1987, X-ray transmission Laue photograph on a large quasi-periodic crystal confirmed the existence of the 5-fold symmetry and the crystallographers. The 1954 Nobel Chemistry Laureate, Prof. Linus Pauling (1901-1994), remained the only prominent opponent to quasiperiodicty in crystals during the last decade of his life.<br /> <br /> In 1992, International Union of Crystallography redefines the crystals as &quot;any solid having an essentially discrete diffraction diagram, and by periodic crystal we mean any crystal in which three dimensional lattice periodicity can be considered to be absent.&quot;<br /> <br /> The main reasons why quasi-periodic crystals were not discovered prior 1982 according to Prof. Shechtman include: the availability of TEM, professionalism, tenacity, belief in self, and courage. He encourages the students to become experts in the fields they like, and they will have great futures.<br /> <br /> <span style="color: #8b4513">This video is adopted from Prof. Dan Shechtman&#39;s speech given to 1,700 high school and university students on May 7, 2012 at National Taipei University of Technology, Taipei, TAIWAN, ROC. [100 years after the commencement of modern crystallography and 30 years after the discovery of quasi-periodic crystals.]</span><br /> <br /> |
| 連結網址 | http://scitechvista.most.gov.tw/zh-tw/Lectures/C/0/50/3/22.htm |