Synthesis of Ultra-Incompressible and Recoverable Carbon Nitrides Featuring CN 4 Tetrahedra.

Carbon nitrides featuring three-dimensional frameworks of CN ₄ tetrahedra are one of the great aspirations of materials science, expected to have a hardness greater than or comparable to diamond. After more than three decades of efforts to synthesize them, no unambiguous evidence of their existence has been delivered. Here, the high-pressure high-temperature synthesis of three carbon-nitrogen compounds, tI14-C ₃ N ₄ , hP126-C ₃ N ₄ , and tI24-CN ₂ , in laser-heated diamond anvil cells, is reported. Their structures are solved and refined using synchrotron single-crystal X-ray diffraction. Physical properties investigations show that these strongly covalently bonded materials, ultra-incompressible and superhard, also possess high energy density, piezoelectric, and photoluminescence properties. The novel carbon nitrides are unique among high-pressure materials, as being produced above 100 GPa they are recoverable in air at ambient conditions.
(© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)