The elastic behavior of dense C3N4 under high pressure: First-principles calculations

• Band gaps of four types of dense C3N4 were widened with the increasing of pressure.
• c-C3N4 has the largest elastic modulus at zero pressure and temperature.
• β-C3N4 will turn to ductile material as external pressure reaches 57 GPa.
• c-C3N4 has a high Vickers hardness of 90.18 GPa.
• Debye temperature of four types of dense C3N4 increase as pressure increases.

We have carried a detailed theoretical study on the geometry, density of states, elastic properties, sound velocities and Debye temperature of α-, β-, c- and p-C3N4 compounds under a maximum of pressure up to 100 GPa by using first principles calculations. The optimized lattice constants under zero pressure and zero temperature agreed well with the previous experimental and theoretical results. The band gaps of the four types of dense C3N4 were widened gradually with the increase of pressure. The calculated Poisson’s ratio γ and B/G values suggest α-, c- and p-C3N4 are brittle materials under 0–100 GPa, whereas β-C3N4 will become a ductile material as external pressure reaches 57 GPa. We found that the Debye temperature of the four dense C3N4 gradually reduces in the order of c-C3N4>p-C3N4>α-C3N4>β-C3N4 at 0 GPa and 0 K. However, the Debye temperature of c-C3N4 was lower than p-C3N4 when external pressure exceeds 6.3 GPa. It may hint that the results could be served as a valuable prediction for further experiments.