Phys. Rev. Lett. 115, 075501 (2015)

Solid materials that have long-range order but no periodicity are known as quasicrystals. They were first observed in 1982 by Dan Shechtman in electron diffraction experiments, a discovery for which he would later be awarded the Nobel Prize in Chemistry. Because of their unusual atomic arrangements, the structures have generated many questions about their growth mechanisms and a variety of theoretical models have been developed. Keiichi Edagawa and colleagues at the University of Tokyo and Tohoku University have now directly observed the growth of a quasicrystal with the help of in situ transmission electron microscopy.

The researchers examined a quasicrystalline alloy made from aluminium, nickel and cobalt (Al70.8Ni19.7Co9.5), which has crystallographically 'forbidden' 10-fold rotational symmetry. A series of high-resolution images were taken with the samples held at 1,183 K, a temperature at which recrystallization can occur. Analysis of the images revealed that the growth process involves frequent structural errors and repairs, and that structures with nearly perfect quasicrystalline order can be obtained. The exact mechanisms by which this growth occurs remain unclear, but Edagawa and colleagues suggest that the process is distinct from ideal models previously proposed.