Dan Shechtman found a forbidden pattern while looking at an aluminium alloy through an electron microscope. Image credit – Wikimedia
When Dan Shechtman analysed the aluminium-manganese alloy rapidly cooled in April 1982 through a transmission electron microscope, the materials scientist found something unusual. The diffraction pattern on the metal revealed the tenfold symmetry, a structure that was thought by scientists not to exist in any crystal.As the National Institute of Standards and Technology (NIST), or as the institute is more popularly known, claimed that Dan Shechtman wrote in his lab notebook a very short and confusing note, “10 fold???”. The findings that started from that one-word entry in the notebook eventually led to the discovery of quasicrystals, a unique material that would revolutionise scientists’ understanding of one of the basic concepts in crystallography.Crystal had always been defined by scientists as having a repetitive atomic pattern. The alloy observed by Shechtman didn’t fall within this definition. Nevertheless, the diffraction pattern showed evidence of long-range order.Why the alloy was considered impossibleAccording to NIST, it is because tenfold symmetry cannot cover space periodically as per the conventional understanding of crystals. However, at first, it was thought that the pattern on the image may be due to something called “twinning,” which can generate such patterns. However, further tests using X-rays disproved this hypothesis.In another NIST article on the subject, it says that the unique structure was proven by repeated tests and eventually led to a new kind of atomic ordering.Birth of QuasicrystalsThe significance of this discovery came from the fact that the alloy itself was neither completely random nor crystalline. Instead, it revealed an ordered structure which wasn’t repetitive, as expected. According to a few studies, the material is an icosahedral aluminium-manganese alloy possessing long-range ordering but not translational periodicity.The significance of such ordering is immense because it means solids can arrange themselves in ways that conventional definitions of crystals do not allow. These kinds of solids are referred to as “quasicrystals.” It initiated a new area of investigation within materials science.
The “impossible” shape, and this opened the door to quasicrystals. Image credit – Wikimedia
Why did scientists resist this discovery?Scientists responded to the finding rather quickly since Shechtman’s discovery was a contradiction to decades of established theory. For many crystallographists, there was nothing that was more contradictory than a non-periodic crystal. The very notion of forbidden symmetry contradicted everything they believed crystals were about.According to NIST historical records, for years, the scientists debated whether the finding was based on a mistake or was evidence of an unprecedented type of matter. Quasicrystals’ presence was independently proven by scientists from France and Japan in 1987 through separate X-ray diffraction analyses. This was precisely what counted, as it became hard to refute the finding as just an error.Implications of the discovery of quasicrystals on materials scienceThere was not only one implication of quasicrystals’ discovery to the field of materials science. There was an entire new area of study that arose thanks to quasicrystals. A study published in Nature Physics states that after quasicrystals’ discovery, decades of scientific studies have been dedicated to researching the symmetries of atoms, metal alloys, and other unusual materials.Moreover, it was revealed that quasicrystals exist not only in novel metal alloys, but also in naturally existing minerals. Quasicrystals possess unique qualities, including hardness, low friction and wear-resistance. The discovery impacted various disciplines outside of crystallography, including condensed matter physics, chemistry, and advanced materials engineering.NIST cite another important piece of Shechtman’s work concerning unusual order of atoms in novel metallic systems.What makes this story relevant today?This story offers a great example of how science advances by taking seriously what appears to be an anomaly. The experiment was very simple, involving the examination of a fast-cooled metal alloy using a microscope, whereupon something strange was noticed. But it became enormously important because the scientist did not ignore the result but rather pursued it, despite its opposition to accepted theory.This story also shows that science is fluid and constantly reinventing its terminology. Far from ruining crystallography, the discovery of quasicrystals provided an occasion for expanding the field’s parameters to include a new kind of order. And ultimately, this discovery earned Shechtman the Nobel Prize in Chemistry in 2011.Since then, nearly four decades have passed, during which time the “10-fold???” has become an iconic symbol of scientific progress – sometimes the biggest breakthroughs occur when scientists don’t ignore facts that seem impossible.
