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Inorganic Chemistry

A glass that isn’t brittle

Alumina glass films can flex and stretch without fracturing

by Prachi Patel
November 14, 2019 | A version of this story appeared in Volume 97, Issue 45


A photo showing the formation of alumina films from plasma.
Credit: Erkka Frankberg
Hitting crystalline alumina with intense laser bursts turns the material into a purple plasma that cools rapidly on a substrate to form an amorphous glassy solid.

Researchers have found that aluminum oxide glass can flex and stretch without breaking (Science 2019, DOI: 10.1126/science.aav1254).

“It basically behaves like a metal,” says Erkka Frankberg, a materials scientist at the Italian Institute of Technology. “This completely changes our point of view on glassy materials.” While the samples the researchers have made are microscopic, if the technique can be translated to a large scale, it might yield glass films that dent like a metal when dropped—and smartphone screens that don’t shatter.

Most glass is made of silica, an amorphous solid in which atoms are arranged haphazardly. Silica glasses are strong, but they are also brittle. Frankberg says this is because of small gaps in the atomic structure. These defects prevent atoms from moving around when the material is stressed. Since its atoms cannot dissipate energy by breaking and forming bonds with their neighbors, glass cracks instead.

Previous studies have hinted that another kind of glass, made from alumina, might exhibit plasticity. Frankberg, Lucile Joly-Pottuz of the University of Lyon, and their colleagues performed a battery of detailed studies to test this idea. The team made 60 nm thick, 2 µm wide alumina films using pulsed laser deposition.

The microscopic films could stretch by 8% and compress to half their size. That might seem small, Frankberg says, but silica glass shows zero ductility. The difference is in the atomic structure. Using transmission electron microscopy and computer simulations, the researchers showed that their alumina glass has a tightly packed, defect-free atomic network. The atoms “can more easily switch places, which is needed for plastic deformation,” Frankberg says.

Translating this work to shatterproof screens could be a long way off. Making large pieces of the material is difficult because, unlike silica, “alumina doesn’t want to be a glass,” Frankberg says. It will require advances in manufacturing and new techniques to make larger, thicker films with the nanoscale structure needed to bring out the material’s ductility.

Nonetheless, “this work clearly provides a guide to chemists on how to design better glasses,” says Antonio Facchetti, a chemist at Northwestern University.

Large-area thin films of flawless alumina glass could make electronics more reliable. And if the findings apply to other glass systems, it could open up entirely new applications, says Hideo Hosono, a materials scientist at the Tokyo Institute of Technology. He points out that amorphous semiconductors such as indium gallium zinc oxide—used in thin-film transistors for liquid crystal display and organic light-emitting diode TVs—belong to this category. “I think this finding implies hidden potential of ionic amorphous materials,” he says.



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