ADVANCED MATERIALS & PROCESSES | OCTOBER 2023 5 NEW GLASS SPORTS SUPREME TOUGHNESS Researchers at the University of Bayreuth, Germany, along with colleagues in the U.S. and China, produced an oxide glass with unmatched toughness. Under high pressures and temperatures, they succeeded in “paracrystallizing” an aluminosilicate glass, with the resulting crystal-like structures creating a highly damage-tolerant material. The new approach begins with oxide glasses that have a disordered internal structure and are the most widely employed commercial glass materials. Using aluminosilicate, which contains silicon, aluminum, boron, and oxygen, the team created a new structure by employing high-pressure and high-temperature technologies. At pressures between 10-15 gigapascals and a temperature of roughly 1000°C, the silicon, aluminum, boron, and oxygen atoms grouped together to form crystal-like structures. These structures are called paracrystalline because they differ significantly from a completely irregular structure, but do not approach the clear regular structure of crystals. Even after a drop RESEARCH TRACKS in pressure and temperature to normal ambient conditions, the paracrystalline structures in the aluminosilicate glass remain. The penetration of the glass with these new structures results in toughness many times higher than be- fore paracrystallization. It now reaches a value of up to 1.99 ± 0.06 MPa (m)¹/², a toughness never before measured for oxide glasses. The team explains the extraordinary strengthening by the fact that forces acting on the glass from outside, which would normally lead to breakage or cracks, are now directed against the paracrystalline structures. They dissolve areas of these structures and transform them back into an amorphous random state. In this way, the glass acquires greater inter- nal plasticity so it does not suffer damage when exposed to strong forces. www.uni-bayreuth.de. BUILDING BETTER THIN-FILM BATTERIES Researchers at Empa, Switzerland, developed a lithium metal-based solid- state battery with some key advantages over today’s lithium-ion technology: It A new solid-state thin-film battery prototype features individual cells measuring just 1 x 3 mm. can be charged and discharged within one minute, lasts about 10 times as long as a lithium-ion battery, and is insensitive to temperature fluctuations. In addition, unlike lithium-ion batteries, it is not flammable. The team now plans to bring this technology to market and has founded a spin-off called BTRY to do so. The battery is a thin-film solid- state battery with a new approach— the researchers succeeded in stacking the thin-film cells on top of each other, increasing their capacity. The thin-film cells are manufactured using vacuum coating. The desired materials are atomized in a vacuum chamber to form individual atoms, which are then deposited in a precisely controlled layer on the target substrate. The high-precision manufacturing method has an additional advantage in that it does not require toxic substances. However, this also makes the thin-film battery more expensive. The researchers see its application primarily in products where the battery only accounts for a small portion of the overall cost, such as smartphones and satellites. Over the next two years, the team plans to increase both the surface area of the battery and the number of layers. www.empa.ch. Simulated structure of glassy (left) and paracrystalline (right) grossular. Oxygen, silicon, aluminum, and calcium atoms (from small to large) are colored lighter the higher the degree of order in the surrounding structure. Courtesy of Hu Tang.
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