A bit of gold grants crystals new electric properties

Crystals can acquire a variety of novel electric qualities when enhanced with just a bit of gold -- or any other noble metal -- according to a study published Wednesday in the journal Nature.

Crystals are not defined by their chemical contents, but by the ordered, symmetrical structure of their molecules -- material scientists like patterned structures, but symmetry, not so much, they say.

"In physics, those materials are rather boring," Marin Alexe, a physicist at the University of Warwick in Britain, said in a news release. "From the point-of-view of functionality, symmetry is not the greatest thing you want to have. You want to break the symmetry in such a way that you would get new effects."

Alexe and his colleagues at Warwick used gold and platinum to break the symmetry of different crystals, yielding new electric effects.

Scientists attached small metal plates to the surface of crystals and supplied the plates with a weak current, creating what's called a Schottky junction.

The electric current excited the semiconductor structure beneath the metal plate, scientists said, enabling several novel effects, like the ability to convert movement or heat into electricity.

"Generally, the properties of these crystals are determined by two factors: the intrinsic properties of the elements that the crystal consists of, and how those elements are arranged to form that crystal, which we call its symmetry," said Mingmin Yang, who conducted the researcher at Warwick, but now works at the RIKEN institute in Japan.

"Our research is demonstrating that how those elements are arranged is not just determined by their own nature, they can also be tuned by external influence," Yang said. "Once we use that influence to change their arrangement, they can exhibit properties that were previously prohibited to them."

The ability to convert force into electricity is called piezoelectric, while the ability to convert temperature changes into electricity is called pyroelectric. Researchers observed both qualities in metal-plated crystals made of Strontium titanate, Titanium dioxide and silicon.

The researchers suggest the breakthrough technology could be used to create extremely sensitive sensors or especially efficient actuators or transducers.

Previous efforts to grant crystal materials new properties have required complicated solid-state chemistry, they said.

"You now have a completely different path to tweak these materials and the ability to tune the effect, something that we have not been able to do before," Alexe said. "That opens the field to many other possibilities with these materials and we might not know where those lead."

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