18 November 1998
The Strange Case Of The Shrinking Solid

Researchers at Lucent Technologies and The Johns Hopkins University have discovered why one ceramic material, zirconium tungstate, shrinks when heated. This phenomenon occurs, the researchers report in the Nov. 12 issue of the journal Nature, because the material's atoms vibrate at low frequencies, causing the material to fold in on itself when heated.

Even though zirconium tungstate was first synthesized in 1959, it largely escaped the interest of scientists until recently. 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.

A common technique used to understand a material's internal vibrations is shooting subatomic particles - such 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 pyramid-shaped building block is untethered and exhibits low vibrational energy. 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.

Because zirconium tungstate can counteract unwanted shrinkage or expansion effects in other materials, it may have industrial applications. One possible application is forming composite-based components in next-generation fiber optic technology for optical networking. "This information about zirconium tungstate is very important," said physicist Art Ramirez of 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 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.

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