June 16, 2021

Quasi-crystals, these materials whose constitution defies the laws of chemistry, were created by a nuclear explosion

July 16, 1945 is not only the beginning of the nuclear age with the first test of an atomic bomb in the Alamogordo desert in New Mexico (United States). The date should now also be marked with a white stone, or rather red, since on that day, a reddish material considered impossible to manufacture by chemists was forged there: a quasi-crystal.

It was found in an ore mined from the 80-meter-wide and 1.4-meter-deep crater caused by the explosion, more powerful than that of the bomb dropped on Hiroshima a few days later. He is described by an American-Italian team in the Proceedings of the American Academy of Sciences of May 17, 2021, of which one of the authors, Paul Steinhardt, was the first, in 1984, to baptize “quasi-crystal” what chemists considered to be a heresy. For them, in fact, a crystal is made up of the periodic repetition of the same pattern. Geometry then imposes rules: it is not possible to pave a room with regular and identical pentagons, while it is possible to do it with squares and hexagons. Likewise, it is not possible to occupy the space with certain repeated volumes.

“Almost impossible”, answered Paul Steinhardt in substance. Just as mathematician Roger Penrose demonstrated that one can pave a floor with multiple patterns to create large-scale ordering, Steinhardt described how to build a large object that looks orderly even while, zooming in on the details , there is no repetition of the patterns. X-rays crossing a quasi-crystal leave in very precise directions, prohibited by the doxa, and testifying to a surprising regularity.

In a meteorite or in a lab

Also a sign of shock for the chemists, who took two years to accept the publication of an article by an Israeli colleague, Dan Shechtman, who made the first quasi-crystal and published the recipe a month before the same word is not used by Steinhardt. The Israeli will be awarded the Nobel in 2011 and more than a hundred quasicrystals have since been made, studied for their catalytic or non-stick coating property.

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Paul Steinhardt specialized in the hunt for quasi-crystals. In 2012, he described the first natural specimen, found in a meteorite 4.5 billion years old. “We had proven that it came from the collision of asteroids in space. Also, in 2016, one of us made quasicrystals in the lab using shock waves. It was then conceivable to look for it in materials around nuclear explosions, explains Luca Bindi, co-author of the discovery, at the University of Florence. However, it took me ten months to find what I was looking for, red trinitite. “ The name refers to Trinity, the site of the explosion, and the rare color comes from the copper in the cables melted during the test.

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