High-Pressure Synthesis of Crystalline Carbon Nitride Imide, C2N2(NH)

摘要

The main-group-element nitrides Si3N4 and Ge3N4 crystallize in at least four polymorphs, including the technologically important α and β forms, a new spinel-type γ phase synthesized at high pressure and temperature, and a high-pressure phase.[1], [2] Sn3N4 also forms a cubic spinel-type phase.[1], [2] There is still no reliable evidence for analogous dense phases of C3N4. High-density C3N4 polymorphs were predicted to have very high bulk modulus and hardness values comparable with or exceeding that of diamond.[3]-[11] Many experimental studies have attempted to produce dense crystalline CxNy phases, by using various techniques, including high-pressure, high-temperature (HP-HT) synthesis. Solids with N:C ratios of 1.3-1.5 have been reported.[1], [2] However, these materials are amorphous or nanocrystalline, and their structures and chemical compositions are not well characterized. Furthermore, the compounds prepared under HP-HT conditions are not generally recovered to ambient conditions.