Tag Archives: quasicrystal

Scientists discover new quasicrystal formed by first-ever nuclear explosion at Trinity Site

The red trinitite sample containing the newly discovered quasicrystal. Credit: Luca Bindi and Paul J. Steinhardt.

On July 16, 1945, the United States Army performed the very first atomic bomb detonation at Trinity Site, New Mexico. The traumatic event obliterated the 30-meter-high test tower, as well as all the miles of copper wires that were connected to measuring and recording instruments. Strikingly, this vaporized debris fused with sand to form a new glassy material known as trinitite, which scientists have recently found at the site — a testament to the devastating, matter-altering power of nuclear weapons.

The red trinitite (Si61Cu30Ca7Fe2) has 5-fold rotational symmetry, which is not possible in a natural crystal. For this reason, it is classed as a “quasicrystal”, exotic materials that do not follow the rules of classical crystallization.

Most crystals are composed of a three-dimensional arrangement of atoms that repeat in an orderly pattern. Depending on their chemical composition, they have different symmetries. For example, atoms arranged in repeating cubes have fourfold symmetry. Atoms arranged as equilateral triangles have threefold symmetries.

Quasicrystals have an atomic structure of the constituent elements, but the pattern is not periodic (it never repeats itself).

They’re remarkable for two reasons: firstly, they’re incredibly rare in nature, and secondly, they’re incredibly unlikely. In fact, when the existence of quasicrystals was first predicted, it cost the career of Daniel Shechtman, the Israeli chemist who first discovered them and lost his job because everyone thought he was mad.

“The head of my lab came to me smiling sheepishly, and put a book on my desk and said: ‘Danny, why don’t you read this and see that it is impossible what you are saying,’” Shechtman, now employed at the Technion – Israel Institute of Technology in Haifa, once recounted.

Shechtman was vindicated decades later after he was awarded the 2011 Nobel Prize in Chemistry.

An aerial view of ground zero 28 hours after the Trinity Test on July 16, 1945. Credit: Los Alamos National Laboratory.

Now, physicists at the Los Alamos National Laboratory have published a new study showing how the extreme shock, temperature, and pressure caused by a nuclear blast can birth new quasicrystals. Using scanning electron microscopy and X-ray diffraction, the researchers revealed the atomic structure of the 20-sided quasicrystal and its five-fold rotational symmetry that used to be considered impossible by conventional standards.

Back-scattered scanning electron microscope image of the sample containing the quasicrystal. Credit: Luca Bindi and Paul J. Steinhardt.

The scientists still don’t know exactly how the trinitite formed step by step, but it seems like the thermodynamic shock under which this quasicrystal formed is comparable to the conditions that led to the formation of natural quasicrystals found in the Khatyrka meteorite, dating back hundreds of millions of year ago.

“This quasicrystal is magnificent in its complexity—but nobody can yet tell us why it was formed in this way. But someday, a scientist or engineer is going to figure that out and the scales will be lifted from our eyes and we will have a thermodynamic explanation for its creation. Then, I hope, we can use that knowledge to better understand nuclear explosions and ultimately lead to a more complete picture of what a nuclear test represents,” said Terry C. Wallace, director emeritus of Los Alamos National Laboratory and co-author of the paper.

This trinitite is effectively the oldest artificial quasicrystal and could someday help scientists better understand illicit nuclear blasts and curb nuclear proliferation.

Extremely rare, unlikely crystal found in Russian meteorite

Scientists have discovered some of the most bizarre crystals in a piece of Russian meteorite. It’s only the third time such a crystal has been found in nature, all three samples coming from the same meteorite.

Image credit: Quasicrystal atomic structure (L), Talapin et al.

The crystals in case are called quasicrystals – structures that have the order characteristic to crystals but don’t share their periodicity. They’re remarkable for two reasons: firstly, they’re incredibly rare in nature and secondly, they’re incredibly unlikely. They’re so unlikely that they cost the scientist who first discovered them his job. Israeli chemist Daniel Shechtman, who first proposed their existence, was considered mad for a long time.

The reason for this seems fairly straightforward – crystals are typically filled with neat shapes like cubes or triangles (four-fold and three-fold symmetry respectively). Other shapes would leave a gap behind. But quasicrystals are arranged in irregular, five-fold symmetry, which should just not work. True story – a few years ago during my undergrad, we were taught that there’s no such thing as five-fold (pentagonal) symmetry.

Pentagonal symmetry. Image credits: J.W. Evans, Ames Laboratory, US Department of Energy

Patricia Thiel, a chemistry and materials science expert based at Iowa State University, used this helpful analogy of tiling a floor to explain the unique properties of quasicrystals in this NPR article:

“If you want to cover your bathroom floor, your tiles can be rectangles or triangles or squares or hexagons,” she said. “Any other simple shape won’t work, because it will leave a gap. In a quasicrystal, imagine atoms are at the points of the objects you’re using. What Danny [Shechtman] discovered is that pentagonal symmetry works.”

So now we know that the strict rules of symmetry can be broken, not only in the lab but also in nature. This sample was found by a team led by geologist Luca Bindi from the University of Florence in Italy.

“What is encouraging is that we have already found three different types of quasicrystals in the same meteorite, and this new one has a chemical composition that has never been seen for a quasicrystal,” one of the team, Paul Steinhardt from Princeton University, told Becky Ferreira at Motherboard.

“That suggests there is more to be found, perhaps more quasicrystals that we did not know were possible before.”

To make things even more interesting, this sample was new and undiscovered. The previous two had been synthesized in a lab, but the latest finding is brand new. It features icosahedral symmetry, an exotic pattern featuring 60 points of rotational symmetry, somewhat like that of a soccer ball.

But while quasicrystals are relatively simple to make in a lab nowadays, we still haven’t found that many in nature. Paul Steinhardt, who serves as the Albert Einstein professor at the science at Princeton University, was one of the authors of the new research. He says that one of the reasons we haven’t found any more of them is because almost no one is really looking.

“There are perhaps one or two other groups [of researchers] at most searching,” Steinhardt said. “Since we found an example, we have been focusing on understanding how this particular one formed since that will tell us something about the likelihood of finding others. But it is very very early times for these kinds of studies.”

The discovery of quasicrystals —crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Scanning tunneling microscopy image (measuring 15 nm x 10 nm) showing individual surface atoms in a new two-dimensional quasicrystal. (c) Wolf Widdra

2-D quasicrystals discovered by accident: chem structure not that impossible it seems

The discovery of quasicrystals —crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Scanning tunneling microscopy image (measuring 15 nm x 10 nm) showing individual surface atoms in a new two-dimensional quasicrystal. (c)  Wolf Widdra

The discovery of quasicrystals —crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Scanning tunneling microscopy image (measuring 15 nm x 10 nm) showing individual surface atoms in a new two-dimensional quasicrystal. (c) Wolf Widdra

Scientists from Germany have developed by accident a peculiar new substance consisting of 12-sided, non-repeating atomic units. Typically this weird structure is called a quasicrystal, a chemical structure thought impossible a few decades ago. Pioneering work on this subject landed Professor Daniel Shechtman the Nobel Prize for Chemistry in 2011.

Klaus Meinel, Stefan Forster and Wolf Widdra, scientists  at Germany’s Martin Luther University, were making trials with an interface made out of two materials under various conditions to engineer properties not found in nature (meta-material). Totally by accident, the team ended up replicating the conditions necessary for the formation of a quasicrystal – crystals that break all the rules of being a crystal at all. Quasicrystals are structural forms that are ordered but not periodic. They form patterns that fill all the space though they lack translational symmetry.

Most crystals are composed of a three-dimensional arrangement of atoms that repeat in an orderly pattern. Depending on their chemical composition, they have different symmetries. For example, atoms arranged in repeating cubes have fourfold symmetry. Atoms arranged as equilateral triangles have threefold symmetries. But quasicrystals behave differently than other crystals. They have an orderly pattern that includes pentagons, fivefold shapes, but unlike other crystals, the pattern never repeats itself exactly.

A crystal that shouldn’t exist

Neither repetitive, nor disorganized in structural quasicrystals have bewildered and astonished scientists. Shechtman, the scientist who first worked with these peculiar structures and who was awarded the Nobel Prize for Chemistry in 2011, was ridiculed for his ideas and findings. Quasicrystals requires extremely precise conditions to form, including vacuum and an argon atmosphere. This has prompted many to claim these are improbable to find in nature. In 2007, however, Shechtman and geologist Luca Bindi from the University of Florence discovered strange quasicrystal-like formations inside a rock from Bindi’s collection. The rock in question was actually a meteorite, and following analysis indeed confirmed that the scientists were looking at quasicrystals. The researchers proved in 2012 that the crystals were formed in space by astrophysical phenomenonae, and not as a consequence of Earth collision or atmosphere entry. This demonstrated that quasicrystals could be found anywhere in the Universe.

Model building blocks of the  12-sided quasicrystal. (c) Wolf Widdra

Model building blocks of the 12-sided quasicrystal. (c) Wolf Widdra

In Germany, the Martin Luther Uni scientists were studying how a certain kind of mineral called perovskite behaved when layered atop metallic platinum. The perovskite film was heated to high temperature. Upon inspection they found a 12-fold symmetry pattern – something that was thought to be impossible. Forster tried to resolve the 12-fold pattern, which clearly now was possible sitting right in front of them, into two groups with six-fold symmetry. It wasn’t possible. The only viable explanation was that they   had created a thin, two-dimensional quasicrystalline layer.

“We were very surprised,” Widdra said. “It took quite a while until we were convinced that we had a new form of two-dimensional quasicrystal.”

The resulting quasicrystal is made out of  12-sided, dodecagonal arrangements with internal patterns of squares, triangles, and rhomboids. “They have a perfect order, but never repeat themselves,” Widdra said.

“This is another beautiful example of just how commonly quasicrystalline structures form,” said physicist Alan Goldman of Iowa State University and the U.S. Department of Energy’s Ames Laboratory, who was not involved in this study. “The number of examples continues to grow and continues to surprise us.”

The actual mechanics of quasicrystal formation are largely unknown so far. Why some materials can retain this structures and other can not is still a mystery.

“We really don’t understand why,” Goldman said. “Each new system provides us with some clues, and the more examples we find, the closer we come to answering that question.”

The 12-sided 2-D quasicrystal was described in a paper published in the journal Nature. [via Wired]

 

The atomic patterns in quasicrystals like this model of an aluminium-palladium-manganese surface exhibit order, but never repeat. (Photo: J.W. Evans, Ames Laboratory, U.S. Department of Energy)

State of matter difference between liquids and solids redefined

What’s the difference between a solid and liquid? You might find this question trivial – naturally, liquids flow and solids… well, they don’t. From a physical point of view, however, things aren’t that simple. Intrigued by some ever so often encountered exceptions in the current accepted theory that describes the differences between the states of matter, scientists have tried to provide a new explanation. American researchers now argue that  the main difference between liquids and solids is the way they respond to shear, or twisting forces and not the way atoms are arranged.

The atomic patterns in quasicrystals like this model of an aluminium-palladium-manganese surface exhibit order, but never repeat. (Photo: J.W. Evans, Ames Laboratory, U.S. Department of Energy)

The atomic patterns in quasicrystals like this model of an aluminium-palladium-manganese surface exhibit order, but never repeat. (Photo: J.W. Evans, Ames Laboratory, U.S. Department of Energy)

The water in the ocean, in liquid state, and a glacier, in solid state, are made out of the same H2O molecules. It’s how the atoms are arranged that governs what state of matter water will hold, or so classic textbooks have it. In liquids, atoms slosh around freely, while in solids the atoms are locked together in a crystal lattice. Because this crystal lattice is so stable, it needs a considerable amount of energy for the atoms to break rank.

This theory of rigidity fails to account for a number of exceptions – too many to remain unnoticed. For instance, it  fails to account for quasicrystals — bizarre solids first discovered in the lab in 1982 and found in nature in 2009, which are arranged in patterns that never repeat, but the material is nonetheless rigid. Glass, one of the most familiar materials, is classed as amorphous – noncrystalline solid in which the atoms and molecules are not organized in a definite lattice pattern – and behaves like a solid, but if one looks closely enough it looks more like a liquid frozen in time.

“Glasses have been around for thousands of years,” said Daniel Stein, a professor of physics and mathematics at New York University. “Chemists understand them. Engineers understand them. From the point of view of physics, we don’t understand them. Why are they rigid?”

Even glaciers can’t be rigidly classified, since their atoms still flow, albeit very slowly. Even liquid water seems rigid if it collides with an object dropped from a large distance or if it’s crossed at high speeds. All these problems have prompted scientists to look for new ways to define the physical differences between liquids and solids, and a team of researchers from France and America believe they have pinpointed a more precise factor to mark the transition between the two states of matter – the way they respond to shear.

Response to shear delimits solids from liquids

Liquids pose minimal resistance to shear and can be twisted in any manner, while solids, even glass or quasi-crystals, pose resistance to shear in an attempt to maintain their shape. The liquid-solid phase transition should thus be marked, the researchers say, by the “shear response” of a material jumping from zero to a positive value.

Physicists typically make their phase boundary calculations for a material through an oversimplified model which assumes the material is boundless – otherwise, in their defense, things would take forever to complete. Unfortunately, this simplification ignores the shape of the material, making it difficult to determine whether the shape will change in response to shear.

Charles Radin, a mathematical physicist at the University of Texas at Austin, and his former student, David Aristoff, now a mathematician at the University of Minnesota built a 2-D model material in which atoms are represented by disks: At low densities corresponding to the material’s liquid phase, it showed no response to shear, but when the disks were densely packed, like the atoms in a solid, shear caused the material to expand. “The crossover where it shows this effect is exactly the density where the system becomes crystalline,” Radin said. “We propose this as a different way of understanding what a solid is.”

Meanwhile, in France, took an alternative route to describe the phase boundary and reasoned that the difference between solids and liquids is the rate at which they flow. Glass, though by all means a solid, still flows, very slowly that is. Even diamonds flow- their atoms that is, as some hop between defects or empty spots in the crystal lattice. To see a diamond flowing under the pull of Earth’s gravity, “one would have probably to wait more than the age of the universe,” said Giulio Biroli of the Institute of Theoretical Physics at CEA in Paris.

The researchers hypothesized that glass would fall somewhere in between a crystalline solid and a liquid by exhibiting a large but finite viscosity under small shear.

“Our ways are complementary,” said Biroli, of the American and French approaches. “If we take both of them, I think we start to understand the difference between a solid and a liquid.”

Nobel prize for chemistry awarded for the discovery of the structure of quasicrystals

The Nobel Prize has been awarded to a single scientist, which is less common than you might think, for the discovery of the structure of quasicrystals.

When this new structure was first proposed, to say that it stirred controversy would be putting it light; at first, the idea was so outside of the general consensus, that his own research group kicked him out. Daniel Shechtman, from Technion – Israel Institute of Technology in Haifa received the top award that can be awarded in chemistry, thus cleaning his name and making up for the years in which he was disconsidered and even ridiculed by his own peers. As mister Shechtman recalls, pretty much nobody from the scientific communitiy believed in him:

“The head of my lab came to me smiling sheepishly, and put a book on my desk and said: ‘Danny, why don’t you read this and see that it is impossible what you are saying,'”

Still, he published the results, and it was only after that that all hell broke loose. He was told he was a disgrace for his research group and asked to leave.

However, time proved him right, and quasicrystals sparkled quite a lot of interest, and Professor David Phillips, president of the Royal Society of Chemistry called them ‘quite beautiful’. He also added:

“Quasicrystals are a fascinating aspect of chemical and material science – crystals that break all the rules of being a crystal at all.”

Quasicrystals are structural forms that are ordered but not periodic. They form patterns that fill all the space though they lack translational symmetry.

In other Nobel news, Tuesday’s award for physics went to Saul Perlmutter and Adam Riess of the US and Brian Schmidt of Australia, who will divide the prize for their discovery that our Universe’s expansion is accelerating.