Nov. 12, 1998 Murray Hill, N.J. -- Most materials shrink when cooled and expand when heated, but researchers at Lucent Technologies and The Johns Hopkins University have discovered why a ceramic material has totally opposite behavior over the largest recorded temperature range, they report in the Nov. 12 issue of Nature.
Although several materials exhibit the same unusual phenomenon as zirconium tungstate, it is the only one that both shows the behavior around room temperature and acts peculiarly at a constant clip. (The overall shrinkage or expansion rate is 0.0005 percent for each degree from -375 degrees to 700 degrees Fahrenheit.)
For those reasons, zirconium tungstate may have industrial applications because it can counteract unwanted shrinkage or expansion effects in other materials. One possible application is forming composite-based components in next-generation fiber optic technology for optical networking.
Even though zirconium tungstate was first synthesized in 1959, it largely escaped the interest of scientists until recently. In 1968, for instance, researchers at Penn State University discovered the material's peculiar properties, but ignored the finding because they were looking for materials that did not expand or shrink at all. Then, two years ago, Oregon State University researchers realized that the material had the uniquely constant qualities over the wide temperature range.
Although scientists knew the atomic structure of zirconium tungstate, they did not understand the material's inner workings, such as how its atoms moved around. This information is crucial when scientists are trying to make new materials with similar properties.
A common technique used to understand a material's internal vibrations is shooting subatomic particles -- known as neutrons -- at its atoms and then recording the speeds and angles at which the particles fly off. Based on these neutron scattering experiments, the researchers discovered that the material vibrates at very low frequencies.
One explanation for the unusually low frequency is that one corner, or atom, of the material's building block, which resembles a pyramid, is untethered. And as temperatures increase, this untethered atom begins pulling in its neighboring atoms, and the overall structure shrinks. Meanwhile, in a closely packed structure, which occurs in most materials, atoms repel each other as temperatures increase because there are no available spaces, and the material expands.
"This information about zirconium tungstate is very important," said physicist Art Ramirez of Bell Labs, Lucent's research and development arm, "because it eventually might lead to making materials with similar properties, but at a reduced cost and perhaps with greater ease."
Currently, Lucent is evaluating a zirconium tungstate composite material - developed by Bell Labs ceramic engineer Debra Fleming -- as a potential packaging material for a "filter," or grating, used in glass optical fiber. The material's unique shrinkage properties would compensate exactly for variations in the glass fiber as temperatures change. Otherwise, multiple wavelengths, or channels, of light transmitted through a fiber would become a scrambled mess. This will be especially important as the number of transmission channels - a process known as Dense Wave-Division Multiplexing - continues to grow, thus boosting the capacity of fiber optic transmissions.
The other authors of the Nature article include physicist Gabriele Ernst and chemist Glen Kowach of Bell Labs and physicist Collin Broholm of Johns Hopkins in Baltimore. The experiments were performed at the Center for Neutron Research at the National Institute of Standards and Technology, Gaithersburg, Md.
Lucent Technologies (LU) designs, builds, and delivers a wide range of public and private networks, communications systems and software, consumer and business telephone systems and microelectronics components. Bell Labs is the research and development arm of the company. For more information about Lucent Technologies, headquartered at Murray Hill, N.J., visit our web site at http://www.lucent.com.
The Johns Hopkins University, an international center for both undergraduate and graduate study and research, is a privately endowed, coeducational institution based in Baltimore, with facilities throughout the Baltimore-Washington area and abroad. Johns Hopkins University news releases can be found at http://www.jhu.edu/news_info/news/
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