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.

了解高压行为对于高温陶瓷的工程应用非常重要。然而，MoC 碳化物在高压下的机械和热力学性能尚不清楚。在这里，我们应用第一性原理方法研究了高压对三种 MoC 碳化物的结构稳定性、弹性模量、硬度、弹性各向异性和德拜温度的影响。选择高压下的立方相和六方相。结果表明，计算得到的高压下生成焓遵循六方晶系（P-6  m2）<六方晶系（ P63/mmc）<立方晶系。重要的是，发现六角形 ( P-6  m2) 与立方和六方 ( P63/mmc ) MoC 相比，MoC 具有更好的热力学稳定性。虽然三种 MoC 的弹性模量随压力增加而增加，但三种 MoC 的硬度随压力增加而降低。特别是，六方（P-6  m2）MoC 的弹性模量和硬度高于立方 MoC。此外，高压导致六角形 ( P-6  m2 ) MoC 从脆性到韧性转变。自然地，六角形 ( P-6  m2 ) MoC 的高弹性模量和硬度由网络 Mo C 键决定。最后，计算出六方晶系的德拜温度（P-6  m2) MoC在高压下高于立方MoC。