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Shahani Group/University of Michigan

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Quasic crystals are a unique class of materials with great promise for practical applications due to their unusual properties. But progress toward realizing that commercial potential has been hindered by the fact that normal manufacturing processes for quasicrystals are prone to producing defects in the form of tiny cracks between crystals known as grain boundaries. a new paper The study, published in the journal Nature Communications, found that under certain conditions, quasicrystals can heal themselves – potentially reviving commercial interest in these materials.

The earliest quasic crystals found were metal alloys, usually aluminum with one or more other metals. This has made them useful for a handful of practical applications, such as non-stick coatings for frying pans and anti-corrosive coatings for surgical instruments. But scientists would prefer to create more complex quasicrystals that are capable of, for example, manipulating light to create new types of camouflage or cloaking.

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“One of the reasons the industry abandoned quasicrystals is because they are full of defects,” Co-writer Ashwin Shahani said, A materials scientist at the University of Michigan. “But we’re hoping to bring quasicrystals back into the mainstream. And this work hints that it can be done.”

As I have written earlier, definition of crystal Assumes a precisely symmetric sequence of atoms in a periodic pattern that repeats over and over again in a 3D lattice. The patterns look the same no matter which direction you look at them, but the quasicrystals are different. They clearly follow mathematical rules, but each cell has a slightly different configuration of adjacent cells, rather than repeating in the same pattern. It is this unique structure that gives quasicrystals their unusual properties.

Think about tiling the bathroom floor. Tiles can only be in certain symmetrical shapes (triangle, square, or hexagon); Otherwise, you won’t be able to fit them together without leaving gaps or overlapping tiles. Pentagons, icosahedrons, and different symmetries with similar shapes that are never exactly repeated will simply not work—except in the case of quasicrystals, where nature dictated them. could Work. The trick is to fill in the gaps with other types of atomic shapes to create an unlikely aperiodic structure.

An Israeli physicist named Daniel Schechtman won the 2011 Nobel Prize in Chemistry for his discovery of quasic crystals in rapidly quenched aluminum alloys in 1982. Princeton physicist Paul Steinhardt discovered the first known naturally occurring quasicrystals in 2008. In 2018, chemist at Brown University created a new type of self-assembling quasicrystals from a single type of nanoparticle: a tetrahedral (pyramid-shaped) quantum dot.

These nanoparticles are also anisotropic, that is, they have different properties depending on their orientation relative to each other. When placed on a liquid surface, they assemble into ten-sided structures called decagons, and these decagons stitch themselves together to form a quasicrystal lattice with tenfold symmetry. What makes this work is the flexible edges of the decades, which can level At key points to convert to polygons with 5, 6, 7, 8, or 9 sides – whatever is necessary to fill in the inevitable gaps between decimals to form a semi-crystal.

X-ray topography visualization showing a side view of two quasic crystals as they begin to melt together during cooling.
Shahani Group/University of Michigan

Earlier this year, scientists from the University of Utah demonstrated that Ultrasound waves can be used to arrange carbon nanoparticles in water in a periodic pattern similar to those found in quasicrystals. And in May, Steinhardt and several colleagues announced Discovery of a previously unknown quasicrystal In red trinitite from the first detonation of an atomic bomb. Even better, researchers can determine where and how the quasic crystals formed thanks to the historical record from the Manhattan Project.

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