Search for Advanced Materials Aided by New Symmetry

April 13, 2011

Researchers say that a new type of symmetry in the structure of proteins, polymers, minerals, and engineered materials increases the chances of discovering and designing new materials.

Four types of symmetries—rotation, inversion, rotation inversion, and translation—have been known for thousands of years. A fifth type, time reversal, was discovered about 60 years ago. Now a sixth type, rotation reversal, increases the number of known ways components of crystalline materials can be combined in symmetrical ways to more than 17,800.

"We mathematically combined the new rotation-reversal symmetry with the previous five symmetries and now we know that symmetrical groups can form in crystalline materials in a much larger number of ways," said Daniel B. Litvin and Venkatraman Gopalan (Pennsylvania State University).

"Rotation reversal is an absolutely new approach that is different in that it acts on a static component of the material's structure, not on the whole structure all at once," Litvin indicated. "It is important to look at symmetries in materials because symmetry dictates all natural laws in our physical universe."

"We found that rotation-reversal symmetry also exists in paired structures where the partner components lean toward each other, then away from each other in paired patterns symmetrically throughout a material," Gopalan said. These "tilting octahedral" structures are common in a variety of crystalline materials, where the component structures are interconnected by networks of shared atoms.

The researchers say it is possible that components of materials with rotation-reversal symmetry could be engineered to function as on/off switches for a variety of novel applications. "We have done some predictions, we will test those predictions experimentally," Litvin said. "We are in the very early stages of implementing the results we have described in our new theory paper." Their work will be published in Nature Materials (May 2011).

Source: Penn State Science (April 3, 2011)

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1092

Start Date:

Wednesday, April 13, 2011