• Abrikosov, Igor A.
• Tasnádi, Ferenc
• Néri, Adrien
• Schnick, Wolfgang
• Wright, Jonathan
• Giacobbe, Carlotta
• Fedotenko, Timofey
• Khandarkhaeva, Saiana
• Weck, Gunnar
• Yin, Yuqing
• Ponomareva, Alena V.
• Akbar, Fariia Iasmin
• Prakapenka, Vitali
• Winkler, Bjoern
• Chariton, Stella
• Mezouar, Mohamed
• Dubrovinskaia, Natalia
• Aslandukov, Andrey
• Dubrovinsky, Leonid
• Pakhomova, Anna
• Wehinger, Björn
• Laniel, Dominique
• Garbarino, Gaston
• Milman, Victor
• Trybel, Florian

Abstract

More than thirty years ago, carbon nitrides featuring 3D frameworks of tetrahedral CN4 units were identified as one of the great aspirations of materials science, expected to have a hardness greater than or comparable to diamond. Since then, no unambiguous experimental evidence of their existence has been delivered. Here, we report the high-pressure high-temperature synthesis of the long-sought-after covalent carbon nitrides, tI14-C3N4, hP126-C3N4, and tI24-CN2, in laser-heated diamond anvil cells. Their structures were solved and refined using synchrotron single-crystal X-ray diffraction. In these solids, carbon atoms, all sp3-hybridized, and nitrogen atoms are fully saturated, forming four and three covalent bonds, respectively, leading to three-dimensional arrangements of corner-sharing CN4 tetrahedra. These carbon nitrides are ultra-incompressible, with hP126-C3N4 and tI24-CN2 even rivalling diamond's incompressibility, and superhard. These novel compounds are recoverable to ambient conditions in crystalline form and chemically stable in air. Being wide-band gap semiconductors with intriguing features in their electronic structure, they are expected to exhibit multiple exceptional functionalities besides their mechanical properties, opening new perspectives for materials science.

Topics

• compound
• Carbon
• x-ray diffraction
• semiconductor
• Nitrogen
• nitride
• hardness
• forming