Evolution of mechanical and thermal properties of diamond under external stress

Diamond exhibits ultra hardness and thermal conductivity, which makes it widely utilized in industrial cutting, electronic devices, and laser technology, where these applications typically require diamond to maintain excellent performance under extreme conditions. Ultimate strength, hardness, and fracture toughness are key parameters that determine its durability. Investigating the evolution of mechanical properties under stress provides deeper insights into its deformation mechanisms and failure modes in extreme environments, facilitating the optimization of diamond for high-stress applications. For thermal properties, the high thermal conductivity makes it highly valuable for heat dissipation in electronic and photonic devices. Stress can change the mechanisms of phonon induced by lattice vibration within the diamond, leading to changes in its thermal conductivity. Understanding these variations can further enhance its heat dissipation capabilities in high-power devices. In this paper, the comprehensive mechanical and thermal properties of diamond under uniaxial stress and hydrostatic pressure are investigated systematically based on the first-principles. The elastic constants including Young's modulus, bulk modulus, shear modulus and Poisson's ratio enhance with the compressive stress and diminish with the tensile stress. The isotropy of bulk modulus is broken due to the deformation of different directions under external stress. Based on the elastic constants, it demonstrates that the mechanical properties of diamond enhance with the compressive stress and diminish with the tensile stress. The thermal properties including Debye temperature, sound velocity (longitudinal, transverse and average velocity) and minimum thermal conductivity also enhance with the compressive stress and diminish with the tensile stress. The fundamental reason for the above phenomenon is that applied stress changes the lattice structure of diamond. And the structural symmetry of diamond is broken along with the redistribution of charge around C atoms, that leads to a new equilibrium state. The phonons that contribute to the thermal conductivity also change with stress. These theoretical results provide valuable insights into the influence of stress on the mechanical and thermal properties of diamond. We also provide basic theoretical practical guidance for the use of Raman laser in diamond under high stress environment.