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

Abstract

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 ₃N ₄, hP126‐C ₃N 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.