Quasicrystal

An Ultra-Rare Crystal Is Found in a Meteorite, Revealing a Bizarre Form of Matter

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IN BRIEF
  • Just a few micrometers in diameter, this quasicrystal is the third to be found in this particular meteorite, but it differs from the other two in both structure and chemical composition.
  • While many applications have been discovered for synthetic quasicrystals, the rarity of naturally occurring ones has made them difficult to study.

ULTRA-RARE SPECIMEN

A team led by Luca Bindi, a geologist from the University of Florence, has found an ultra-rare quasicrystal just a few micrometres wide in a meteorite that landed in Russia five years ago. The discovery has been detailed in Scientific Reports.

Two other quasicrystals have already been discovered in this particular meteorite, but the latest is different from its predecessors in both structure and chemical composition. This new quasicrystal is composed of aluminum, copper, and iron atoms structured in an arrangement very similar to the pentagon-based pattern of a soccer ball, a first of its kind in nature.

“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,” says Paul Steinhardt, a team member from Princeton, in an interview with Motherboard. “That suggests there is more to be found, perhaps more quasicrystals that we did not know were possible before.”

WHAT IS A QUASICRYSTAL?

At the time of their discovery in the 1980s, quasicrystals defied what we thought we knew about crystallography.

Regular crystals such as diamonds and snowflakes are made up of atoms in almost-perfect symmetry, while polycrystals such as metals and ice have more random structures that closely resemble amorphous solids like glass and most plastics. Quasicrystals, however, have an ordered yet never repeating arrangement of atoms. Their unique atomic structures fuse the symmetrical properties of regular crystals with the chaos of amorphous solids.

Quasicrystals can easily be artificially synthesized in labs, and in the three decades since their discovery, scientists have found many useful applications for them, incorporating quasicrystals into LEDs, frying pans, and other objects. Their rarity in nature, however, makes the study of organic quasicrystals still largely uncharted territory, so this new discovery could tell us a lot about this strange form of matter.

Researchers discover new form of 12-sided quasicrystal.

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A team of researchers working at Germany‘s Martin-Luther-Universität has discovered a new form of a 12-sidded quasicrystal. In their paper published in the journal Nature, the team describes how they accidently created the previously unknown crystalline structured material while investigating interfacing properties between various substances.

Researchers discover new form of 12-sided quasicrystal

Quasicrystals are substances that look a lot like crystals but have one major exception—the  of their structure is non-repeating. They were first discovered in 1982 by Daniel Shechtman—he won the Nobel Prize in chemistry for it in 2011. Since that time they have been created in the lab in various ways and have even been found in nature—as part of a meteorite that fell in Russia (which because it was found to have been created by a non-heat related astrophysical process, showed that applying heat wasn’t necessary to create them). In this latest effort the researchers created one using perovskite oxides, potentially extending the number of  that can be created by such .

The team in Germany was investigating the ways perovskite behaved when used as a layer on top of a metal base. After exposure to extremely high temperatures, they noted that the material began to shape into a pattern, which they naturally assumed was a crystal. Upon closer inspection, they found that the 12-sided pattern didn’t repeat itself—the mark of a . The team notes that perovskite oxides are not normally noted for forming into quasicrystals, and in fact, no one really thought it was possible.

The discovery extends the types of quasicrystals that are known to exist, though not all of them have 12 sides of course. Their unusual structures make possible the creation of materials with unusual properties which scientists are just now beginning to find. Finding ways to create them using materials not normally associated with such odd structures may pave the way to a much broader array of end products—now that scientists know that it is possible, the door has been opened to creating all sorts of new materials from perovskite oxide based quasicrystals (now called barium titanate), such as thermal insulators or coatings for electronic components.


Abstract

The discovery of quasicrystals—crystalline structures that show order while lacking periodicity—forced a paradigm shift in crystallography. Initially limited to intermetallic systems, the observation of quasicrystalline structures has recently expanded to include ‘soft’ quasicrystals in the fields of colloidal and supermolecular chemistry. Here we report an aperiodic oxide that grows as a two-dimensional quasicrystal on a periodic single-element substrate. On a Pt(111) substrate with 3-fold symmetry, the perovskite barium titanate BaTiO3 forms a high-temperature interface-driven structure with 12-fold symmetry. The building blocks of this dodecagonal structure assemble with the theoretically predicted Stampfli–Gähler tiling having a fundamental length-scale of 0.69?nm. This example of interface-driven formation of ultrathin quasicrystals from a typical periodic perovskite oxide potentially extends the quasicrystal concept to a broader range of materials. In addition, it demonstrates that frustration at the interface between two periodic materials can drive a thin film into an aperiodic quasicrystalline phase, as proposed previously. Such structures might also find use as ultrathin buffer layers for the accommodation of large lattice mismatches in conventional epitaxy.




 

Like Father, Like Son.

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A 10-year-old boy spends his summer vacation helping his chemist dad solve the structure of complicated materials.

Chemist Sven Hovmöller of Stockholm University had been trying for nearly a decade to determine the structures of materials known as quasicrystals and their nearly identical approximants. Thought to be physically impossible until some 30 years ago, quasicrystals are aperiodic structures—meaning they don’t display the rigidly repeating patterns characteristic of crystals like sodium chloride, for example. Since their discovery in the lab, physicists had been working tirelessly to better understand the structure of quasicrystals. But because the existence of such materials was doubted for so long, computer programs currently used to interpret imaging data aren’t equipped to analyze the aperiodic structures.

Hovmöller has worked on and off in the field of quasicrystals for more than 25 years, focusing primarily on the aluminum-cobalt-nickel (Al-Co-Ni) system. Like other quasicrystal researchers, he studied not the elusive materials themselves but their approximants, which differ in atom placement by only 1 or 2 percent and have more tractable patterns of atomic arrangement. Hovmöller’s interest in quasicrystals was piqued when he saw a conference poster displaying an electron diffraction pattern of one of the Al-Co-Ni approximants. The image was “so beautiful, so clear, [that] it should be possible to solve it,” recalls Hovmöller, who immediately invited Markus Döblinger, the student who made the poster, to do a postdoc in his lab.

But after months of further electron microscopy studies, the duo couldn’t seem to solve the structure. “Not only him and me, but other people also involved, tried so hard, but we didn’t get anywhere,” Hovmöller recalls. “It was extremely annoying.”

The image was so beautiful, so clear, that it should be possible to solve it.
—Sven Hovmöller, Stockholm University

Döblinger eventually moved on to the University of Munich, but Hovmöller couldn’t let the idea go. “Every year, once or twice, I [tried] to solve these things, and I just couldn’t.” Then, last summer, he had a seemingly off-the-wall idea. He’d enlist the aid of his 10-year-old son, Linus. “I thought, He’s a smart guy; maybe he could help me,” Hovmöller says.

The father-and-son team sat at the kitchen table for 2 days, poring over the dozens of electron microscopy images Döblinger had generated, as well as some electron diffraction data, which provides more precise information on the materials’ atomic positions. Hovmöller would explain to Linus what he was thinking about how the images all fit together, and when Linus didn’t understand something, he’d interrupt his father to ask. This made Hovmöller realize that he was rushing to conclusions. When he slowed down to clear up Linus’s confusion, he’d get new ideas. “In 2 days, we solved four new structures.”

They published their findings in a special issue of Philosophical Transactions of the Royal Society A honoring the 85th birthday of Alan Mackay, who had predicted the existence of quasicrystals before they were identified in 1982. Linus was listed as a coauthor on the paper (370:2949-59, 2012).

“A kid [who] is clever and good at spatial things might well come up with a solution to a problem like that,” says surface physicist Renee Diehl of Penn State University. “I think there’s probably a lot of potential in 10-year-old kids that we’re not tapping.”

And in fact, Linus isn’t as unlikely a character as one might expect in the field of quasicrystals. “There have been a lot of highly creative and unusual people associated with the field,” says Carnegie Mellon University theoretical physicist Mike Widom. Amateur mathematician Robert Ammann, for example, made several significant contributions to quasicrystal theory before the crystals were even proven to exist. Others have pointed to the links between quasicrystals and art, such as aperiodic tilings and mosaics found in Persia. There’s even a company, called Zometool, that manufactures toys used to model quasicrystalline shapes, Widom notes. “The field is quite rich … [in] unusual personalities,” he says. “This boy is in the tradition of the field attracting some nontraditional scientists.”

But all the structures of the Al-Co-Ni quasicrystal and its approximants aren’t exactly solved. “What Sven Hovmöller did is quite nice,” says Walter Steurer of the Laboratory of Crystallography at ETH Zurich, but his methods are qualitative. Thus, Hovmöller and Linus merely mapped out some of the repeating motifs in four of the approximant structures, but “did not publish any atomic coordinates.” The precise locations of some of the crystals’ atoms have yet to be pinpointed.

“A lot of the interesting controversy in the field of quasicrystals has to do with fairly fine details,” which are critically important to understanding the materials’ true structures, Widom says. “You can know where 90 percent of the atoms are, but still not really know the structure because a minority of the atoms are doing interesting and crucial things. . . . What [Hovmöller and Linus] give us is a good starting point for future structure refinement.”

But if someone eventually solves the true structure of the Al-Co-Ni quasicrystal or its approximants, it won’t be Linus. “He’s refused” to work on the remaining structures, Hovmöller says with a laugh. “He’s still a little bit tired” from the last bout of structure solving.

http://www.sciencedaily.com