The discovery of quasicrystals through rapid quenching of metallic alloys

A completely unexpected structure was discovered at the National Bureau of Standards by Dan Shechtman working with rapidly solidified AlMn alloys. Transmission electron microscopy studies showed dendritic crystals with an icosahedral diffraction pattern of sharp spots. The symmetry of the pattern implies that the structure cannot be periodic; the sharp spots indicated a translational order that approximates what mathematicians call quasiperiodicity. The structures have become known as quasicrystals.

Since the initial discovery a large number of systems have yielded quasicrystals by a variety of processing methods. There is even one ternary system AlLiCu in which the quasicrystal is a stable, rather than a metastable phase. At least one other symmetry (decagonal) has been observed and there are indications that there may be more than one crystal structure with icosahedral symmetry.