Atomic structure of ultrasound material not what anyone expected
by Staff Writers
Raleigh, NC (SPX) Feb 26, 2018
Lead magnesium niobate (PMN) is a prototypical "relaxor" material, used in a wide variety of applications, from ultrasound to sonar. Researchers have now used state-of-the-art microscopy techniques to see exactly how atoms are arranged in PMN - and it's not what anyone expected.
"This work gives us information we can use to better understand how and why PMN behaves the way it does - and possibly other relaxor materials as well," says James LeBeau, an associate professor of materials science and engineering at North Carolina State University and corresponding author of a paper on the work.
"What we've found is that the arrangement of atoms in PMN gradually shift along a gradient, from areas of high order to areas of low order; this happens throughout the material," LeBeau says. "That's substantially different than what conventional wisdom predicted, which was there would be alternating areas of high order and no order, right next to each other."
This information can be fed into computational models to provide new insights into how PMN's atomic structure influences its characteristics.
"This won't happen overnight, but we're optimistic that this may be a step toward the development of processes that create PMN materials with microstructures tailored to emphasize the most desirable characteristics for ultrasound, sonar or other applications," LeBeau says.
"It could also potentially offer insights into the role of atomic structure in other relaxor materials, providing similar long-term benefits for the entire class of materials."
The paper, "Gradient chemical order in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3," is published in the journal Applied Physics Letters. Lead author of the paper is Matthew Cabral, a Ph.D. student at NC State. The paper was co-authored by Elizabeth Dickey, a professor of materials science and engineering at NC State; and Shujun Zhang, a professor at the University of Wollongong.
Breaking local symmetry: Why water freezes but silica forms a glass
Tokyo, Japan (SPX) Feb 20, 2018
Everyone knows that water freezes at 0C. Life on Earth would be vastly different if this were not so. However, many are less familiar with water's cousin, silica, whose wayward behavior when cooled has long puzzled scientists. Unlike water, silica (SiO2) does not freeze easily. When liquid silica cools, its atoms fail to arrange into an ordered crystal. Instead, as temperature decreases, the liquid state survives even far below the nominal freezing temperature; this phenomenon is termed supercooli ... read more
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