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In 2015, researchers watched a decagonal Al–Ni–Co quasicrystal grow inside a high-resolution electron microscope. The images showed that growth was not flawless: errors appeared at the advancing edge, and some were repaired as more layers formed. The final structure had nearly perfect quasicrystalline order. The team proposed that a process called phason relaxation helps explain that repair.
What makes quasicrystal growth puzzling?
Ordinary crystals can be described by a unit cell that repeats throughout the material. Quasicrystals have long-range order without that simple repeating pattern: their arrangement is quasiperiodic. The challenge is to explain how local interactions among atoms can produce an ordered structure that does not grow by repeating one basic unit. The 2015 paper framed this as a central question in understanding quasicrystal formation. Read the paper in Physical Review Letters.
What did the researchers observe?
Keisuke Nagao, Tomoaki Inuzuka, Kazue Nishimoto and Keiichi Edagawa studied an Al–Ni–Co decagonal quasicrystal using in-situ, high-temperature, high-resolution transmission electron microscopy. A contemporary account gives the sample composition as Al70.8Ni19.7Co9.5 and says the thin sample was heated to 1183 K to induce recrystallization. The researchers recorded its growth and analyzed tiling patterns extracted from a sequence of images. Chemistry World’s 2015 report describes the experiment.
The image sequence and tiling analysis indicated that faults appeared at the growth front. After additional layers formed, atomic clusters could rearrange, correcting some earlier errors. The authors described frequent error-and-repair processes and reported that the final grown structure showed nearly perfect quasicrystalline order. They did not publish a numerical error rate or a count of repairs in the sources cited here, so the result should be understood qualitatively rather than as a measured percentage.
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How might repair produce long-range order?
The researchers proposed that phason relaxation contributes to the correction of growth errors. In this interpretation, rearrangements during growth help the structure move toward ideal quasicrystalline order. The images support the observed pattern of errors followed by repair; phason relaxation is the authors’ proposed explanation for how that repair helps create the final order, not a directly settled mechanism. The contemporary report said the physical mechanism of the repair was unclear at the time.
How does this compare with local growth-rule models?
The observation challenged one proposed account, not every theory of quasicrystal growth. Edagawa said, “In our case, the quasicrystals do not grow according to Steinhardt’s model.” Paul Steinhardt replied that his rules were designed for “a mathematical abstraction of tiles,” whereas this experiment concerned a three-element alloy and growth constrained to one direction. Those differences limit what the experiment can establish about abstract models or other materials.
Other scientists emphasized different implications. Primož Ziherl said the result supported the possibility that perfect quasicrystals can self-assemble without atoms slotting into prearranged positions, suggesting that non-local forces are not necessary. Steinhardt called empirical verification of possible perfect growth “an important development,” while maintaining the distinction between his mathematical model and the alloy experiment. These are attributed interpretations of the finding, not a settled consensus on how all quasicrystals grow.
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- It shows: one specific Al–Ni–Co decagonal quasicrystal was observed growing in situ, with frequent errors and subsequent repair inferred from the image sequence and tiling analysis.
- It supports: the possibility that repair during growth helps a real material reach nearly perfect quasicrystalline order.
- It does not establish: a universal growth mechanism, a numerical frequency of defects or repairs, or the refutation of all local growth theories.
- Its scope is specific: the alloy composition and the experiment’s one-direction growth constraint matter when comparing the result with mathematical tilings or other growth conditions.
When was the result published?
The paper by Nagao and colleagues appeared in Physical Review Letters, volume 115, article 075501, on 10 August 2015. It is a dated experimental result, not by itself evidence about the latest state of quasicrystal-growth research.
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