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Persistence pays off for crystal chemist

Discovery of mosaic material wins Nobel prize.

A quasicrystal’s atomic structure never quite repeats itself, as shown in this computer simulation. Credit: E. Heller/SPL

As Louis Pasteur famously pointed out: "In the fields of observation, chance favours only the prepared mind." Stumbling across a curiosity is not enough — understanding it, and convincing the world of its importance, are key.

Dan Shechtman at the Technion Israel Institute of Technology in Haifa knows this only too well. Last week he was awarded the Nobel Prize in Chemistry for his 1982 observations of quasicrystals: materials with a mosaic-like atomic array that never quite repeats, thus flouting the established rules of crystal structure (see 'Chemistry's lone heroes').

Yet Shechtman was not the first to spot evidence of the crystals. "Given the relative simplicity of making these materials, it is certain that they would have been seen by numerous scientists before, who dismissed them because they didn't fit the rigid rules of crystallography," says Veit Elser, a physicist at Cornell University in Ithaca, New York.

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Click for chemistry's lone heroes.

Indeed, in 1979, Marc van Sande, a 27-year-old doctoral student working in the Electron Microscopy for Materials Science (EMAT) group at the University of Antwerp, Belgium, had recorded electron diffraction patterns from metal alloys that showed clear evidence of quasicrystals. Close to the end of his PhD, van Sande just filed the confusing patterns in the EMAT library: he was keen to take up his new job with the Belgian materials-technology company Umicore, where he is now an executive vice-president.

"We were making so many new discoveries every week with the high-resolution electron microscopes that the more awkward things were set aside," recalls van Sande. "I'm realistic about it: seeing the pattern is a long way from investigating it and publishing it."

Shechtman, unaware of van Sande's work, observed similar odd diffraction patterns about three years later — and grasped their importance. He had the self-belief to plough on with his work, despite the scorn of luminaries such as chemist and two-time Nobel prizewinner Linus Pauling. "If you have repeated your observations and are sure you are correct, then listen to others but don't give up because people tell you 'this cannot be'," Shechtman told Nature.

Dan Shechtman: “People didn’t believe me.” Credit: U. Sinai/Getty Images

Thirty years ago, scientists were taught that all crystalline materials were composed of atoms packed into regularly repeating three-dimensional lattices, such as the hexagonal honeycomb of a beehive. This definition dictated that the lattice must have basic repeating units with particular symmetries: these units could be rotated by one-half, one-quarter or one-sixth of a full circle and still look the same. Pentagonal symmetry was ruled out, because no perfectly regular lattice could exhibit it.

On 8 April 1982, Shechtman, who was on sabbatical at the US National Bureau of Standards (now the National Institute of Standards and Technology, NIST) in Gaithersburg, Maryland, found that an artificial alloy of aluminium and manganese disobeyed the rules.

When he shot electrons through the material, they created a regular diffraction pattern, apparently proving that the material's atomic structure consisted of orderly repeating elements. But that pattern showed a forbidden symmetry — it could be rotated by both one-tenth and one-fifth of a full circle and would still look the same. In his laboratory notebook, Shechtman wrote: "10 Fold???"

Others did their best to persuade him that his discovery was wrong. "People didn't believe me," he says, adding that his dogged pursuit of the problem even led his group director to suggest he move to another team. Shechtman finally got his findings published in November 1984, along with Ilan Blech, a materials scientist at Technion; John Cahn, a physicist at NIST; and Denis Gratias, a crystallographer then at the Centre for Metallurgic Chemistry in Vitry, France (D. Shechtman et al. Phys. Rev. Lett. 53, 1951–1953; 1984).

By chance, mathematicians Paul Steinhardt and Dov Levine — both then at the University of Pennsylvania in Philadelphia — were at the same time completing a rigorous theory of the three-dimensional version of mathematical curios known as Penrose tilings, structures with an apparent five-fold symmetry that were created by British mathematician Roger Penrose in the 1970s. Steinhardt coined the term 'quasicrystals' for the resulting structures: neither classically periodic crystals, nor a glass-like mess of disordered atoms. They were what Shechtman had seen in his metallic alloy.

Other examples soon flooded in from around the globe. In 2009, Steinhardt and other researchers reported the first quasi­crystal structure to be seen in a natural material: an alloy of aluminium, copper and iron reported to have come from 200-million-year-old rocks in Russia's Koryak Mountains (L. Bindi et al. Science 324, 1306–1309; 2009).

It still isn't clear how atoms assemble into quasicrystal structures, and the discovery has found few real-world applications. However, quasicrystals do have potential: they are very hard, are poor at conducting heat and electricity, and have non-stick surfaces. But Shechtman's key contribution to chemistry lies in opening scientists' eyes to the possibility of new forms of matter, notes Sven Lidin, an inorganic chemist at Stockholm University and a member of the Nobel Committee for Chemistry. As Lidin wrote in his description of the award: "The discovery of quasicrystals has taught us humility."

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Van Noorden, R. Persistence pays off for crystal chemist. Nature 478, 165–166 (2011). https://doi.org/10.1038/478165a

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