Quasicrystals in the act of growing have for the first time been recorded by Japanese researchers using high-resolution transmission electron microscopy, answering a mechanical dilemma of chemistry with an “error-and-correction” observation.

“For the first time, we succeeded in observing the quasicrystal growth directly,” University of Tokyo’s Dr. Keiichi Edagawa told The Speaker. “By the direct observation, we obtained [a] picture of formation.”

The researchers heated a two-dimensional quasicrystal sample of aluminum, nickel, and cobalt (Al70.8Ni19.7Co9.5) at temperatures between 1123 and 1183 Kelvins.

Using HRTEM, the researchers put together a series of images of the sample as the quasicrystals transformed under heat.

The composite video illustrates the researchers’ main finding:
Quasicrystals, at least in the decagonal phase observed, grow according to an “error-and-correction” pattern.

The team observed a quasicrystal grain growing into the space left by another shrinking quasicrystal grain.

The action takes place in the middle of the growing and shrinking grains — a region known as the “growth front.” There, atomic clusters appear as a row of tiles being flipped, breaking the long-range quasiperiodic order of the lattice and resulting in disorder.

However, as more rearrangements take place over time, the disordered clusters correct, sometimes after several rows have grown incorrectly.

Dr. Keichi Edagawa

Dr. Keiichi Edagawa

“Quasicrystals grow with frequent error-and-repair, where the repair process corresponds to the relaxation of so-called phason strain,” Edagawa told us. “No strict local growth rules are at work, which is somewhat different from the ideal growth models previously proposed theoretically.”

What drives the errors and corrections during growth is still not known. Also unknown remains whether the phenomena observed also takes place in other quasicrystal phases.

The report, “Experimental Observation of Quasicrystal Growth,” was completed by University of Tokyo and Tohoku University researchers Drs. Keisuke Nagao, Tomoaki Inuzuka, Kazue Nishimoto, and Keiichi Edagawa, and was published online in APS Physics.

By Justin Munce