After more than three decades of work, scientists believe they have created a nearly unbreakable material that rivals diamond as the hardest substance on Earth. An international team led by researchers at the University of Edinburgh's Center for Extreme Conditions Science has made a breakthrough by synthesizing precursors of carbon and nitrogen to create a carbon nitride that is harder than cubic boron nitride, currently the second-hardest material after diamond.
Dominique Laniel of the University of Edinburgh said: "In discovering the first new carbon nitride material, we are in disbelief that a material that researchers have dreamed of for the past three decades is finally available. These materials provide a powerful impetus to bridge the gap between high-pressure materials synthesis and industrial applications."
While scientists recognized the potential of carbonitrides as early as the 1980s, including their high heat resistance, creating them was another story. In fact, until now, no credible studies have been conducted on their synthesis.
The researchers pointed out in the research report: "Carbonitrides with a three-dimensional framework of CN4 tetrahedrons are a great wish of materials science."
The research team, which also included materials experts from the University of Bayreuth in Germany and Linköping University in Sweden, achieved the feat by subjecting different forms of carbon-nitrogen precursors to pressures of 70-135 gigapascals (or one million times atmospheric pressure) while heating them to more than 1,500°C (2,732°F).
The atomic arrangement was then examined using X-ray beams at the European Synchrotron Research Facility in France, the Deutsche Electron Synchrotron in Germany and the Advanced Photon Source in the United States.
The analysis showed that the synthesized carbon nitride compounds contained three structures required for breakthrough superhard materials. The scientists were then surprised to find that the three compounds retained their superhard properties after cooling and returning to ambient pressure.
The team believes this breakthrough paves the way for a variety of uses, including protective coatings for vehicles and spacecraft, powerful cutting tools and photodetectors.
"These materials not only excel in their versatility but also show that technologically relevant phases can be recovered from synthetic pressure conditions equivalent to thousands of kilometers inside the Earth. We are convinced that this collaborative research will open up new possibilities in the field," says Florian Trybel, Assistant Professor at Linköping University.
While the functional scope of this incompressible carbon nitride compound is not yet known, the researchers also found that the compound has photoluminescent, piezoelectric and high-energy-density properties, enabling it to store large amounts of energy with a small amount of mass.
The researchers stated in the research report: "Physical property studies show that these strong covalent bond materials are ultra-incompressible and ultra-hard, as well as have high energy density, piezoelectric and photoluminescence properties. The new carbonitrides are unique among high-pressure materials because they are produced at pressures above 100GPa and can be restored under ambient conditions in the air."
The research was published in the journal Advanced Materials.