First rejected as impossible, discovery has changed basic notions
The discovery of a crystal whose atoms are packed in a pattern that never repeats has won Israeli scientist Daniel Shechtman the 2011 Nobel Prize in chemistry. The structures in quasicrystals, as they are known today, are similar but never exactly identical. This patterning is found in 800-year-old Islamic tiling and described in the mathematical sets of English mathematician Roger Penrose, but was thought to be forbidden in matter.
"He discovered something nobody thought possible," says chemical engineer Nancy Jackson. "But he stuck to his guns and with time researchers found that this unique crystal structure was actually right," says Jackson, president of the American Chemical Society.
Shechtman will take home $1.5 million for the discovery.
Quasicrystals are exceedingly strong and are found in particular blends of steel used to make razor blades and surgical instruments. These crystals are also slippery like Teflon and scientists are investigating them for use in coatings for frying pans. Poor conductors of heat, quasicrystals may prove also useful as heat insulators for engines or in devices such as light-emitting diodes.
Shechtman, 70, of the Technion–Israel Institute of Technology in Haifa, made the discovery one April morning in 1982 while investigating a mix of aluminum and manganese. At the time Shechtman was working at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology). Many in the scientific community scoffed at the initial discovery, and the research wasn't accepted for publication in a scientific journal until 1984.
But eventually, Shechtman's finding forced science to change the definition of a crystal from "a substance in which the constituent atoms, molecules or ions are packed in a regularly ordered, repeating three-dimensional pattern" to "any solid having an essentially discrete diffraction pattern."
Most states of matter are either well behaved and orderly or a disordered mess. Quasicrystals are peculiar because they fall in between — they are regular but never repeating. When Shechtman made his discovery he had just quickly cooled a glowing hot metal, which should have yielded disorder among the atoms. But when he looked at the diffraction pattern created when electrons scattered off his material, he saw something orderly.
“I looked at the material and it looked very strange to me,” Shechtman said in an interview last year.
Not only was it orderly, but the pattern of dots had an unheard of symmetry. Think of dividing a square with two intersecting lines to get four equal parts. Rotate the square 90 degrees and it looks the same. Rotate it another 90 degrees and it still looks the same. When something can be rotated four times and look exactly the same, it has fourfold symmetry. Prior to Shechtman’s discovery, scientists thought crystals could have only one, two, three, four or sixfold symmetry. But the atoms in his metal had fivefold symmetry.
“Lo and behold, I see a diffraction pattern that has fivefold rotational symmetry,” he said. “I said, ‘No, it cannot be.’ ”
Shechtman said the work was initially met with ridicule. The head of his lab brought him a basic textbook on crystallography, suggesting he read up on the subject. Shechtman was later expelled from the lab.
But once the discovery was finally published, “people jumped on it immediately,” says materials scientist John W. Cahn, a NIST colleague and coauthor of the original paper. Other crystallographers who had observed similar patterns without grasping their meaning revisited old lab notes. Further reports of crystals with forbidden symmetry followed.
In 2009, naturally occurring quasicrystals were discovered for the first time, in a mineral sample from a Russian river.
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