The stability and decomposition of graphitic C3N4 (g-C3N4) were studied in the pressure and temperature range of 10-25 GPa and up to 2000°C by multi-anvil experiments and phase characterization of the quenched products. g-C3N4 was found to remain stable at relatively mild temperatures, but decomposes to graphite and nitrogen at temperatures above 600-700°C and up to 15 GPa, while it decomposes directly to diamond (plus nitrogen) above 800-900°C and between 22 and 25 GPa. The estimated decomposition curve for g-C 3N4 has a positive slope (~ 0.05 GPa/K) up to ~ 22 GPa, but becomes inverted (negative) above this pressure. The diamond formed through decomposition is characterized by euhedral crystals which are not sintered to each other, but loosely aggregated, suggesting the crystallization in a liquid (nitrogen) medium. The nitrogen release from the graphitic CN framework may also play an important role in lowering the activation energy required for diamond formation and enhancing the grain growth rate. No phase transition of g-C 3N4 was found in the studied P-T range.
ASJC Scopus subject areas
- 化学 (全般)