Pressure induced structural, hardness, elastic and thermodynamic properties of three MoC

Insight into the high pressure behavior is very important for the engineering applications of high temperature ceramics. However, the mechanical and thermodynamic properties of MoC carbide under high pressure are unknown. Here, we apply the first-principles approach to study the influence of high pressure on the structural stability, elastic modulus, hardness, elastic anisotropy and Debye temperature of three MoC carbides. The cubic and hexagonal phases under high pressure are selected. The results show that the calculated formation enthalpy under high pressure follows the sequence of hexagonal (P-6 m2) < hexagonal (P63/mmc) < cubic. Importantly, it is found that the hexagonal (P-6 m2) MoC has better thermodynamic stability in comparison to the cubic and the hexagonal (P63/mmc) MoC. Although the elastic modulus of three MoC increases with increasing pressure, the hardness of three MoC decreases with increasing pressure. In particular, the elastic modulus and hardness of the hexagonal (P-6 m2) MoC are higher than the cubic MoC. In addition, the high pressure results in brittle-to-ductile transition of the hexagonal (P-6 m2) MoC. Naturally, the high elastic modulus and hardness of the hexagonal (P-6 m2) MoC are determined by the network MoC bonds. Finally, the calculated Debye temperature of the hexagonal (P-6 m2) MoC is higher than the cubic MoC under high pressure.