We finally understand why quasicrystals can exist

The quasi -cristals are rare and strange, but the researchers have now shown that they can be the most stable configuration for certain atoms – and why they can exist.

In crystals, atoms form predictable grids, which makes them very stable. In glass – both the ordinary type that constitutes drinking glasses and more exotic glasses like the obsidian formed in volcanoes – atoms do not follow any order. The glasses are metastable, therefore a change in their environment such as heating or small impurities of some wandering atoms of the bad element, can make them become a different type of matter. Given enough time, all that is atomically amorphous to be classified as a glass will also end up crystallize.

But the quasi -cristals ride the environment – their atoms are arranged in models, but these models never repeat themselves – and the way they remain stable have long been a question mark.

Wenhao Sun at the University of Michigan and his colleagues have now used advanced computer simulations to find the answer. They focused on two known quasi-cristals, one made from scandium and zinc and the other of yterbium and cadmium, and simulated a series of nanoparticles of increasingly large quasi-cristals. At each stage, they calculated the energy of the quasi-cristals and compared it to the energies that the atoms would have in more conventional crystal-type arrangements.

The laws of physics dictate that most stable objects are made of atoms whose collective energy is as weak as possible, and this is exactly what researchers have found – the strange quascistal was favored compared to the more common atomic structures because the energy necessary to maintain it was low.

Sun says it was somewhat unexpected because comparison with glass often leads physicists to intudate that quasi-cristals should be metastable. They were previously difficult to understand because advanced simulation methods tend to assume perfectly periodic arrangements of atoms, explains Vikram Gavini, member of the team at the University of Michigan. The researchers have used an innovative computer approach, and their simulations have shown that the growth of laboratory quasi-cristals would require very specific conditions, which is not unexpected because they are rarely found in the wild.

“Quasi-cristals have extraordinary vibrational properties, which are linked to thermal conductivity and thermoelectric effects. With the new method, we could be able to study them, ”explains Peter Bommemer at the University of Warwick in the United Kingdom. “Maybe the next supermateral will be discovered not in a laboratory but on a computer.”