Scientists have solved a decades-long puzzle and unveiled a near unbreakable substance that could rival diamond as the hardest material on earth, a new study says.

A research team from Scotland, Germany, and Sweden has found that when carbon and nitrogen precursors are subjected to extreme heat and pressure, the resulting materials, known as carbon nitrides, are tougher than cubic boron nitride, the second-hardest material after diamond.

The breakthrough opens doors for multifunctional materials to be used for industrial purposes including protective coatings for cars and spaceships, high-endurance cutting tools, solar panels, and photodetectors, the experts say.

Materials researchers have attempted to unlock the potential of carbon nitrides since the 1980s, when scientists first noticed their exceptional properties, including high resistance to heat. Yet, after more than three decades of research and multiple attempts to synthesize them, no credible results were reported.

Now, an international team of scientists, led by researchers from the Center for Science at Extreme Conditions at the University of Edinburgh and experts from the University of Bayreuth, Germany, and the University of Linkoping, Sweden, have finally achieved a breakthrough.

The team subjected various forms of carbon nitrogen precursors to pressures between 70 and 135 gigapascals -- around one million times our atmospheric pressure -- while heating them to temperatures of more than 1,500 degrees C.

To identify the atomic arrangement of the compounds under these conditions, the samples were illuminated by an intense X-ray beam at three particle accelerators: the European Synchrotron Research Facility in France, the Deutsches Elektronen-Synchrotron in Germany, and the Advanced Photon Source based in the United States.

The researchers discovered that three carbon nitride compounds were found to have the necessary building blocks for super hardness. Remarkably, all three compounds retained their diamond-like qualities when they returned to ambient pressure and temperature conditions.

Further calculations and experiments suggest the new materials contain additional properties including photoluminescence and high energy density, where a large amount of energy can be stored in a small amount of mass.

Researchers say the potential applications of these ultra-incompressible carbon nitrides is vast, potentially positioning them as ultimate engineering materials to rival diamonds.

"These materials provide strong incentive to bridge the gap between high-pressure materials synthesis and industrial applications," said Dr. Dominique Laniel, Future Leaders Fellow, Institute for Condensed Matter Physics and Complex Systems, School of Physics and Astronomy, University of Edinburgh.

The research was published in Advanced Materials.

Source: The University of Edinburgh

Published December 2023