Superhard carbon-rich C–N compounds hidden in compression of the mixture of carbon black and tetracyanoethylene

Abstract

The recent successful synthesis of Pnnm-CN structure inspired researchers to explore new superhard 3D C–N compounds via a similar method, that is, high-pressure and high-temperature experiments involving carbon and nitrogen elements. Naturally, in some past high-pressure experiments involving C–N precursors, whether there are undiscovered C–N compounds in the product is worthy of being re-examined. This work proposed four novel carbon-rich C–N compounds, namely, r-C17N4, sc-C4N, sc-C17N4–I, and sc-C17N4-II, which possibly coexist with the unidentified simple cubic carbon phase in the shock compression products of the carbon black and tetracyanoethylene mixture. Most of the X-ray diffraction peaks from the experiment could be understood by the proposed C–N compounds. Furthermore, the calculations of formation enthalpies using experimental materials as precursors show that these four C–N compounds are more easily synthesized than the carbon structures previously used to explain the unknown phase. These phenomena indicate that C–N compounds might be synthesized in this experiment, not just the new carbon phase. The current study may provide a new idea for the experimental research of C–N compounds and inspire further research to reevaluate previous experimental findings.