Scientists May Have Discovered a New Class of Solids

A possible discovery published in the journal Physical Review Letters has some reminiscing about the good old days when solids were either categorized as crystal or glass.

Born from small patches of a rapidly cooled mixture of aluminum, iron and silicon, researchers have identified a new substance that refuses any kind of label, first failing to exhibit the extended ordering of atoms indicative of crystal, and second growing outward from "seeds," which glass most certainly does not.

"Very weird. Strangest material I ever saw," materials physicist Lyle Levine of the National Institute of Standards and Technology (NIST) said in a press release.

Dubbed it "q-glass," X-ray diffraction reveals the substance has neither rotational or translational symmetry -- both of which are found in crystal. However, unlike glass, the atomic arrangement does not appear to be random, either.

"As the nodule grows, every atom still knows where to go," Levine said.

Q-glass appears to have a strict chemical composition and when viewed under a microscope can be seen growing outward from a seed during cooling, excluding any atoms that don't fit, much like a crystal would.

"It's rejecting atoms that aren't fitting into the structure, and if there's no structure, it's not going to be doing that," Levine said. "It's amazing. Everything you can think about this thing behaves like a crystal, except it isn't."

In order to rule out other possibilities, the team employed a range of sophisticated techniques at Argonne's Advanced Photon Source.

One theory was that the material might represent a mass of randomly arrayed crystals simply too small to appear individually under the X-ray probes. However, this idea was rejected based on the fact that if such crystals were present, they would grow slowly as the material was heated and then cooled, which was not the case.

"We went through the laundry list of possibilities and disproved them, one by one," Levine said.

Another possibility is "frustration," or when two or more incompatible crystal orderings start growing from the seeds and end up banging up against each other and thwarting any kind of overall order.

And while this option has not yet been ruled out, there is still one more, and that is the "exciting possibility is that the q-glass is the first example of a 3-dimensionally ordered configuration of atoms that possesses neither translational nor rotational symmetry," Levine said.

"Such structures have been theorized by mathematicians, but never before observed in nature."