There’s an intoxicating order to the periodic table that sometimes makes us think we know all the rules of atoms and molecules. Time and time again, though, chemists have proved their own rules wrong, whether it’s by redefining the hydrogen bond or discovering new elements. The Nobel Prize in chemistry, announced today, goes to yet another rule-breaker, a scientist who railed against the prevailing beliefs of his colleagues to redefine what a crystal is.
Daniel Shechtman, a materials scientist at the Technion-Israel Institute of Technology, discovered a strange diffraction pattern in his electron microscope on April 8, 1982. Crystals were defined as atoms in an ordered, repeating pattern, and the pattern Shechtman was looking at was impossible according to his textbooks: It suggested an ordered crystal whose structure didn’t repeat. Later, the structures underlying those patterns, called quasicrystals, were found to have much in common with medieval Islamic mosaics and their nonrepeating patterns.
After persuading his colleagues to take him seriously, Shechtman published his findings, and in 1992, the International Union of Crystallography finally broadened the definition of a crystal to recognize the nonrepeating patterns of quasicrystals.
But quasicrystals aren’t simply a quirk of chemical nomenclature; they’ve been found to have a number of uniquely useful properties. Typical crystals transport heat and electrons well because their regular structure allows for coordinated waves of excitation called phonons. But quasicrystals are poor thermal conductors and good electrical conductors, making them suitable for converting thermal energy into electrical energy. They are now being tested for use in engine insulation and surface coatings for frying pans.
Quasicrystals are also being evaluated as components for light-emitting diodes (LEDs). A number of groups have found that a layer of quasicrystal on the surface of gallium nitride LEDs can enhance light output by redirecting light in the direction needed for a specific application. Traditional crystals can also be used as a coating, but sometimes their regular lattice structure creates spikes in the light beam that have to be diffused. Quasicrystals, researchers contend, may be a good choice for commercial applications like backlit displays and white light illumination.