DAN SHECHTMAN - QUASI-PERIODIC MATERIALS, A PARADIGM SHIFT IN CRYSTALLOGRAPHY

• published: 18 Sep 2015
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Nobel Laureate, Professor Dan Shechtman of Technion, Israeli Institute of Technology gives the Nobel Laureate Lecture "QUASI-PERIODIC CRYSTALS – A PARADIGM SHIFT IN CRYSTALLOGRAPHY": 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 number 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 Icosahedral phase, 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 describe the important role of electron microscopy as an enabling discovery tool. [1] D. Shechtman, I. Blech, Met. Trans. 16A (June 1985) 1005-1012. [2] D. Shechtman, I. Blech, D. Gratias, J.W. Cahn, Phys. Rev. Letters, Vol 53, No. 20 (1984) 1951-1953.Professor and Secretary General of The Royal Danish Academy of Sciences and Letters, Mogens Høgh Jensen, writes about the speaker: Professor Dan Shechtman was awarded the 2011 Nobel Prize in Chemistry for the discovery of quasicrystals. In quasicrystals, one finds the fascinating mosaics of the Arabic world reproduced at the level of atoms: regular patterns that never repeat themselves. The configuration found in quasicrystals was considered impossible, and Professor Shechtman had in 1982 to fight a fierce battle against established science to substantiate his fundamental findings. His discoveries have fundamentally altered how scientists conceive of solid matter. Following Shechtman's discovery, scientists have produced other kinds of quasicrystals in the lab and discovered naturally occurring quasicrystals in mineral samples from a Russian river. Scientists are currently experimenting with using quasicrystals in different products such as frying pans and diesel engines. Dan Shechtman is a Distinguished Professor at Technion, Israel Institute of Technology, and was recently running for the office of President of the State of Israel.