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An international research team led by the University of Bayreuth has discovered a metal that combines electrical conductivity with internal polarity. This enables it to exhibit second harmonic generation—an optical effect typically observed only in non-metals. The finding is of particular interest for sensors and electrical engineering. The research is in the Journal of the American Chemical Society.

Materials that can simultaneously conduct electricity and manipulate light are of great interest to scientists developing modern technologies. For example, these materials may contribute to the development of faster and more energy-efficient computer chips, more precise sensors for medical devices, or new components for optical communication systems.

Research into such materials demonstrates how even simple elements such as magnesium and chlorine can, under extreme conditions, form entirely new compounds with properties previously considered impossible. These could eventually be applied in advanced photonics, quantum devices, or energy technologies.

Recent findings by an international team led by the University of Bayreuth show that the compound magnesium chloride (Mg₃Cl₇) defies conventional rules of metallic behavior. While typical metals conduct electricity via a "sea" of free electrons surrounding their atoms, conductivity in magnesium chloride occurs through electrons provided by chloride ions, making it an anionic metal. This mechanism weakens the usual electrical screening found in metals and allows the compound to maintain a permanent internal separation of charges—a property known as polarity.

Remarkably, this polar metal not only conducts electricity, but when exposed to light, it emits light at twice the frequency. This rare combination of electrical conductivity, polarity, and optical frequency-doubling is not only unusual but also highly valuable for applications in electronics, sensors, and energy systems.

"It is very exciting that we have discovered a metal that not only conducts electricity but also emits light in unexpected ways," says Dr. Yuqing Yin, post-doctoral researcher in the group of Material Â鶹ÒùÔºics and Technology at Extreme Conditions at the University of Bayreuth and lead author of the study. "Such a combination is extremely unusual in nature and opens up entirely new perspectives for the design of multifunctional materials."

The discovery was made under high pressure using a diamond anvil cell—an instrument capable of generating pressures comparable to those found deep inside planets. Using intense synchrotron X-ray beams, the team was able to determine the crystal structure of magnesium chloride in situ, as the material only exists under extreme conditions.

Although it cannot yet be produced in industrial quantities, the discovery opens the door to a new class of materials that combine metallic conductivity with valuable optical properties.

"We are only at the beginning," notes Professor Dr. Leonid Dubrovinsky, researcher at the Bavarian Geoinstitute (BGI) at the University of Bayreuth and senior co-author of the publication. "The principles we have uncovered offer new ways of thinking about chemistry and materials design. Our work shows that even very simple elements like magnesium and chlorine can, under the right conditions, form completely unexpected structures with unique properties."

The study highlights how high-pressure research continues to reveal surprising behaviors in seemingly ordinary elements and compounds. By pushing materials beyond the boundaries of everyday chemistry, scientists are uncovering new rules—and new possibilities—for designing the functional materials of the future.